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The Spyware Used in Intimate Partner Violence

Authors:
The Spyware Used in Intimate Partner Violence
Rahul Chatterjee, Periwinkle Doerfler, Hadas Orgad, Sam Havron§, Jackeline Palmer, Diana Freed,
Karen Levy§, Nicola Dell, Damon McCoy, Thomas Ristenpart
Cornell Tech New York University Technion §Cornell University Hunter College
Abstract—Survivors of intimate partner violence increasingly
report that abusers install spyware on devices to track their
location, monitor communications, and cause emotional and
physical harm. To date there has been only cursory investigation
into the spyware used in such intimate partner surveillance (IPS).
We provide the first in-depth study of the IPS spyware ecosystem.
We design, implement, and evaluate a measurement pipeline that
combines web and app store crawling with machine learning to
find and label apps that are potentially dangerous in IPS contexts.
Ultimately we identify several hundred such IPS-relevant apps.
While we find dozens of overt spyware tools, the majority are
“dual-use” apps — they have a legitimate purpose (e.g., child
safety or anti-theft), but are easily and effectively repurposed
for spying on a partner. We document that a wealth of online
resources are available to educate abusers about exploiting apps
for IPS. We also show how some dual-use app developers are
encouraging their use in IPS via advertisements, blogs, and
customer support services. We analyze existing anti-virus and
anti-spyware tools, which universally fail to identify dual-use
apps as a threat.
I. INTRODUCTION
Intimate partner violence (IPV) affects roughly one-third of
all women and one-sixth of all men in the United States [54].
Increasingly, digital technologies play a key role in IPV
situations, as abusers exploit them to exert control over their
victims. Among the most alarming tools used in IPS are
spyware apps, which abusers install on survivors’ phones in or-
der to surreptitiously monitor their communications, location,
and other data. IPV survivors [23, 29, 46], the professionals
who assist them [29, 58], and the media [9, 22, 37] report
that spyware is a growing threat to the security and safety
of survivors. In the most extreme cases, intimate partner
surveillance (IPS) can lead to physical confrontation, violence,
and even murder [10,18].
The definition of “spyware” is a murky one. Some apps are
overtly branded for surreptitious monitoring, like FlexiSpy [2]
and mSpy [6]. But survivors and professionals report that
other seemingly benign apps, such as family tracking or “Find
My Friends” apps [8, 29, 58], are being actively exploited by
abusers to perform IPS. We call these dual-use apps: they
are designed for some legitimate use case(s), but can also be
repurposed by an abuser for IPS because their functionality
enables another person remote access to a device’s sensors or
data, without the user of the device’s knowledge. Both overt
spyware and dual-use apps are dangerous in IPV contexts.
We provide the first detailed measurement study of mobile
apps usable for IPS. For (potential) victims of IPS, our results
are decidedly depressing. We therefore also discuss a variety
of directions for future work.
Finding IPS spyware. We hypothesize that most abusers find
spyware by searching the web or application stores (mainly,
Google Play Store or Apple’s App Store). We therefore
started by performing a semi-manual crawl of Google search
results. We searched for a small set of terms (e.g., “track my
girlfriend’s phone without them knowing”). In addition to the
results, we collected Google’s suggestions for similar searches
to seed further searches. The cumulative results (over 27,000+
returned URLs) reveal a wide variety of resources aimed at
helping people engage in IPS: blogs reviewing different apps,
how-to guides, and news articles about spyware. We found 23
functional apps not available on any official app store, and a
large number of links to apps available on official app stores.
We therefore design, build, and evaluate a crawling pipeline
for Google Play [3], the official app marketplace for Android.
Our pipeline first gathers a large list of potential IPV-related
search terms by using search recommendations from Play
Store, as we did with Google search. We then collect the top
fifty apps returned for each of the terms. Over a one-month
period, this approach retrieved more than 10,000 apps, though
many have no potential IPS use (e.g., game cheat codes were
returned for the search term “cheat”).
The data set is large enough that manual investigation
is prohibitive, so we build a pruning algorithm that uses
supervised machine learning trained on 1,000 hand-labeled
apps to accurately filter out irrelevant apps based on the
app’s description and the permissions requested by the app.
On a separate set of 200 manually labeled test apps, our
classifier achieves a false positive rate of 8% and false negative
rate of 6%. While we do not think this represents sufficient
accuracy for a standalone detection tool given the safety
risks that false negatives represent in this context, it suffices
for our measurement study. We discuss how one might tune
the pipeline to incorporate manual review to achieve higher
accuracy (and no false negatives), as well as initial experiments
with crowdsourcing to scale manual review.
We performed a smaller study using our measurement
pipeline with Apple’s App Store, and got qualitatively similar
results. See Appendix B.
The IPS landscape. The resulting corpus of apps is large,
with hundreds of Play Store applications capable of facilitating
IPS. We manually investigate in detail a representative subset
of 61 on-store and 9 off-store apps by installing them on
research phones, analyzing the features and user interface they
provide, and observing how they are marketed. We uncover
three broad categories of apps: personal tracking (e.g., find-
my-phone apps), mutual tracking (e.g., family tracking apps),
and subordinate tracking (e.g., child monitoring apps).
The three types of apps have differing capabilities, though
all can be dangerous in an IPS context. The worst allow
covert monitoring of all communications, remote activation of
cameras and microphones, location tracking, and more. Two
of the on-store apps we analyzed, Cerberus and TrackView,
violate Play Store policy by hiding their app icon and showing
no notifications, making them as covert as off-store spyware.
(We reported these apps to Google for review, see discussion
about our disclosures below.) All 70 apps are straightforward
to install and configure, making them easy to use by abusers.
Some off-store apps overtly advertised themselves for use
in IPS. An example is HelloSpy, whose website depicts a
man physically assaulting a woman with surrounding text dis-
cussing the importance of tracking one’s partner, see Figure 1.
Others, including those on the Play Store, most often do
not have descriptions or webpages promoting IPS. However,
further investigation revealed that a number of these apps
advertised or condoned IPS as a use case. We document that
vendors advertise on IPS-related search terms such as “how
to catch cheating girlfriend” on both Google and Play Store.
We also uncover networks of IPS-focused websites that link
exclusively to a specific app’s webpage and directly advertise
IPS use cases for the app.
For a subset of 11 apps (6 on-store and 5 off-store),
we contacted customer service representatives posing as a
potential abuser.1In response to the question “If I use your app
to track my husband will he know that I am tracking him?”,
8 out of 11 responded with affirmative explanations implicitly
condoning IPS. Only one (an off-store app) replied with an
admonishment against use for IPS. Two apps did not respond.
Performance of anti-spyware tools. The existence of so
many easy-to-use, powerful apps usable for IPS demonstrates
that victims need detection and cleanup tools. A variety
of tools advertise their ability to deal with spyware. These
include tools from major anti-virus vendors, such as Symantec,
Kaspersky, and Avast, as well as some lesser-known tools. As
far as we are aware, no one has evaluated any of these tools
for the particular task of detecting IPS spyware or dual-use
apps. We evaluate anti-spyware tools against a corpus of 280
on-store apps detected by our crawl of Google Play (that we
manually verified to be usable for IPS) and all 23 off-store
spyware apps we identified.
No anti-spyware tool effectively detects IPS-relevant apps.
The best performing (Anti Spy Mobile) flagged 95% of off-
store spyware, but only 47% of on-store IPS-relevant apps. The
tool also has a prohibitively high false positive rate of 12%,
labeling applications such as Google Chrome and Play Store as
spyware. The major anti-virus systems were some of the worst
performers for dual-use apps (flagging at most 13% of on-
1Our IRB board confirmed that our experiments are exempt from review,
as they engage people in their professional capacities and do not collect PII.
Fig. 1: Screenshot of the HelloSpy website promoting intimate
partner violence [35].
store apps). While this labeling may be appropriate for other
contexts, for IPV victims these tools are far too conservative.
The tools do better detecting off-store spyware, but still fail
to label some dangerous apps.
Summary and next steps. We perform the first study of
applications usable for IPS. In particular:
We introduce measurement approaches for discovering ap-
plications easily found by abusers via searching the web
and app stores. The discovered apps pose immediate and
dangerous threats to victims.
We highlight the role of dual-use apps in IPS, and show
that they are often as powerful as overt spyware. On-store
apps can achieve prohibited capabilities due to a lack of
OS-level protections.
We show that many apps brand themselves only for “le-
gitimate” purposes, but simultaneously pay for IPS-related
advertisements. A small measurement study revealed that
some apps’ customer service representatives condone IPS.
We show that existing anti-virus and anti-spyware tools are
ineffective at detecting and remediating IPS spyware.
While our first-of-its-kind study has various limitations (see
Section III-D), it nevertheless uncovers the prevalence of
apps that can facilitate IPS, and which can lead to immense
emotional, psychological, and physical harm for victims.
We disclosed our results to Google, and they have already
taken steps to improve safety for their users. Google reviewed
the apps we discovered and confirmed that they took action
against some of the apps that violated Play Store policies due
to a lack of persistent notifications or promotion of spyware
or stealth tracking. In addition, Google is expanding their
restrictions on advertisement serving for IPV-related queries.
We hope our results will motivate the computer security
community more broadly to work to improve survivor safety.
We therefore conclude with an initial discussion about next
steps, including how to: deal with the complexities of dual-
use apps; improve detection tools for use in IPV settings;
suggest ways honest developers can prevent exploitation of
their tools for IPS; and modify laws or regulations to better
help survivors.
2
II. BACKGROUND: SPY WARE I N IPV
Intimate partner violence (IPV) includes physical or sexual
violence, stalking, or psychological harm by a current or
former intimate partner or spouse. A number of studies [23,29,
40,58] indicate that abusers increasingly exploit technology to
monitor and control their partner in IPV contexts, which can
be a form of abuse in and of itself and can facilitate other
forms of abuse (physical, emotional, sexual, etc.).
Much of the IPV literature discusses the installation of IPS
apps on a survivors’ mobile devices [23, 28, 29, 40, 46, 58].
One study [46] interviewed 15 survivors of IPV in the United
States, and found that 20% reported being monitored by
spyware. An analysis of data stolen from two spyware vendors,
FlexiSpy and Retina-X, revealed that 130,000 people use one
of the tools [22]. The hackers’ investigation concluded that
most usage is for IPS. Interviews of survivors and profession-
als working with them indicate that abusers can easily find
spyware via web search, and that many otherwise innocuous
apps, such as “Find my phone” apps and child trackers, are
easily repurposed by abusers for spying on intimate part-
ners [23, 29, 40, 53, 58].
Spyware or other apps that facilitate surveillance are par-
ticularly dangerous in IPV situations because abusers often
have physical access to their partner’s device(s), and can know,
guess, or compel disclosure of access credentials (passwords,
PIN codes, or swipe patterns) [29, 46, 58]. This enables the
abuser to install spyware via an app store such as the Google
Play Store or Apple App Store. In the case of Android, an
abuser can configure the phone to allow installation of apps
not found on the Play Store. Installation of apps does not
require sophisticated technical knowledge and, as we discuss
in detail later, easy-to-follow installation guides are readily
available. All of the spyware we encountered can be used
without rooting the phone, though in some cases additional
spying features were available should one do so.
Types of IPS apps. Our focus is on apps that abusers
purposefully install in order to stalk, monitor, and control an
intimate partner’s device without their consent. The examples
above indicate two main classes of spyware. We refer to
apps like “Find my phone” as dual-use apps, as they can be
deployed as spyware despite not being purposefully designed
for such use. In contrast, overt spyware like FlexiSpy and
Retina-X are designed and advertised to be surreptitious and
applicable for spying on a target.
We will use the term IPS-relevant apps or IPS apps to
refer to apps that we believe may be purposefully installed
by abusers for surveillance; this category includes both overt
spyware and dual-use apps. In more detail we consider as
IPS-relevant apps those (1) whose primary purpose is giving
another person the ability to collect data, track location, and/or
remotely control a device; (2) which function, after initial
installation and configuration, without interaction with the
current user of the device; and (3) that the victim most
likely does not want on the device. This means we will, in
general, not consider apps such as Google Maps: while it can
be configured to continuously update another person of the
device’s location without interaction with the current user, its
primary purpose is not to enable location tracking by another
person and most victims want it installed. Certainly such apps
have safety and privacy implications in IPV, but, particularly
because victims might desire their continued installation, their
analysis and remediation will require different approaches.
These scoping rules will not always be easy to apply in a
decisive way. When in doubt we conservatively marked apps
as IPS relevant. In most such cases we anyway found anecdotal
evidence online of abusers employing the app or similar ones.
Other forms of malware. We do not consider adware
(sometimes called commercial spyware) or other potentially
unwanted programs (PUPs), that help companies collect in-
formation on user behavior. The ecosystem of PUPs has
been analyzed in [38, 56]. Moreover, we don’t specifically
consider advanced malware such as those used by governments
or the remote access trojans (RATs) [25, 39, 43] often used
by voyeurs, which generally would require more technical
sophistication on the part of an abuser to deploy for IPS.
Likewise there have been many prior studies measuring and
detecting more commercially-motivated malware that steal
users secrets (e.g., bank details) [12, 14, 26, 34, 60, 62]. While
in theory it could be that some spyware or anti-spyware apps
double as malware that aims to leak confidential information to
third-parties (people other than the abuser), we have found no
evidence of intention2by vendors to do so. These other forms
of unwanted software certainly carry privacy risks in IPV
contexts as well as elsewhere, but their study and remediation
require different techniques than those we explore here.
Open questions. Despite the many indications that spyware
is widely used in IPV, there has been, to date, no in-depth
study of the technologies available to abusers. Thus, our work
endeavors to answer a number of critical open questions:
How easy is it to find apps usable for IPS? How many such
apps are available?
Can we find and categorize the kinds of dual-use apps that
might be used in IPS?
What capabilities are available to abusers?
Are app developers encouraging IPS?
Are there effective tools (e.g., anti-spyware) for detecting
and removing such apps?
III. FINDING IPS-REL EVANT APPS
In this section, we perform measurements to discover apps
usable for IPS. We focus on the apps that an abuser, assumed to
be of average technical sophistication, could locate and deploy.
To this end, we ignore apps that are difficult to locate (e.g.,
advertised in closed forums) or difficult to deploy (e.g., require
rooting a phone). We instead look at apps that can be readily
2Some spyware apps do have vulnerabilities that accidentally leak data to
third-parties, see Section IV.
3
found by searching either in a popular search engine such as
Google or in an official app store.
We emulate a hypothetical abuser seeking apps for IPS. We
hypothesize that most abusers begin by performing searches
such as “track my wife” or “read SMS from another phone”
in a search engine. Under this hypothesis, we gather exam-
ples of both resources for abusers (such as how-to guides)
and apps readily found by abusers. While our measurement
methodology may not uncover all IPS apps, we believe it
surfaces a representative sample of apps as used by abusers
because: (1) our approach uncovers a huge number of IPS
tools that (2) cover in aggregate all the types of tools reported
by survivors [16, 29, 40].
Below we describe our methodology for searching in greater
detail. For concreteness and because of its large market share,
we focus on the Android ecosystem, specifically using search
interfaces provided by Google.com and Google Play. Our
techniques can be applied to other ecosystems that provide
a search engine; see Appendix B for our treatment of Apple.
Methodology. To perform searches, we need a wide-ranging
list of queries that an abuser might use. For this, we utilize
query recommendation APIs provided by search engines, such
as a query completion API (provided by Google Play) and a
related query API (obtained by parsing the search results page
of Google). A query completion API responds with a number
of recommended search phrases that contain the submitted
query as a substring, whereas a related query API responds
with a set of search phrases believed to be semantically related
to the submission. In both cases the intent of the APIs is to
suggest related search phrases as educated by prior searches
made by other users of the engine.
We use a query snowballing approach to find a large set of
useful queries given a small set of queries as a seed set. The
procedure is straightforward: query the recommendation APIs
on all queries in the seed set, collect the resulting recommen-
dations, query the resulting recommended search terms, and
continue until some predetermined number of queries have
been discovered (e.g., `=10,000 search phrases), or until we
converge to a set where no new recommendations are found.
More on query snowballing is given in Appendix A.
A. Searching for IPS on Google
We begin by applying our query snowballing to the Google
search engine. We used the Python Requests library [17] to
make the queries and download the results, and the Lxml
library [5] to parse the pages. Search results vary based on,
among many other factors, the query browser and the search
history. We used a user-agent identifying the request as from
a Chrome browser on Linux and disallowed any client-side
cookies to minimize influence of historical searches.
Google’s related query suggestions provide semantically
close queries, so we use in our seed set relatively long and
complete queries, as opposed to the smaller seed terms we use
for Google Play (see below). We begin with queries such as,
“how to catch my cheating spouse” or “track my husband’s
Type Description # Example
Blogs How-to blogs for IPS 21 best-mobile-spy.com
Videos How-to videos for IPS 12 youtube.com
Forums Q&A forums for IPS 7 quora.com
News News about using spying software 2 theguardian.com
Downloads Pages hosting IPS apps 12 download.cnet.com
App sites Websites of apps 5 thetruthspy.com
App store Link to apps in the official app stores 2 GPS Phone Tracker
Other Irrelevant pages 39 amazon.com
Fig. 2: Types of websites found in manual analysis of 100 randomly
sampled URLs from our 27,741 URLs found via Google search.
phone without them knowing.” The returned suggestions are
not always relevant to our study, e.g., suggestions for “cheat”
include suggestions related to cheat codes for video games. We
therefore filter the queries using regular expression blacklists
(built via manual inspection). The initial set of seed queries
and the blacklists used are given in Appendix A.
Our snowballing process did not converge even after con-
sidering query sets of sizes up to `=10,000, therefore we
consider all 10,000 query recommendations. We submitted
each of these queries to Google and recorded the top 10 results
for each query. From these searches, we collected 27,741
URLs on 7,167 unique domains. We manually investigated a
random subset of 100 URLs to group their associated websites
into six major categories; see Figure 2. Nearly two-thirds of
the sampled pages are directly related to IPS, with only 39
URLs linking to unrelated content. We now discuss the 61
IPS-related URLs, first those that provide information about
how to engage in IPS, and then those that link to IPS apps.
Information about conducting IPS. The majority of the IPS-
related URLs (65%) link to blogs, videos, or question-and-
answer forums discussing how to engage in IPS. The blogs
describe how to use one or more tools to spy on someone.
Example blog post topics include “Read your wife’s messages
without touching her phone” on a blog linking to mSpy and
“These apps can help you catch a cheating spouse” appearing
on the NY Post news site. News articles that came up in our
searches also point to incidents of spyware being used for
IPS. All these serve to direct those wanting to engage in IPS
to app websites, even should that website try to distance itself
from IPS. We discuss more about disingenuous blogging in
Section V. The video tutorials (mostly hosted on Youtube)
similarly explain how to setup and use apps for spying.
The question-and-answer forums focus on spying or track-
ing with discussions about how to use various tools for spying
on intimate partners. For example, in one forum an (ab)user
posts “I’m looking for an app I can install on my wife’s phone that
is hidden so that I can see where she is or has been via cell towers
or gps.In reply, another (ab)user posts,
[Install] Cerberus from the market. Once installed and
configured, can be set to be invisible in the app drawer.
You can also record audio and take pictures remotely with
it! Be sure to silence the camera first though!
IPS apps. The remaining IPS-related URLs linked to home
pages for apps, links to Google Play application pages, or
4
websites that aggregate a number of download links for apps.
From the Google search results and in the resulting web pages,
we collected 2,249 unique URLs pointing to Google Play
(extracted using regular expression search), among these URLs
we found 1,629 active apps listed in Google Play. Manual
analysis of a random sample of 100 of these apps revealed
that 22 were usable for IPS. All of which were separately
discovered by our search in the Play store (see Section III-B).
The prevalence of Google Play links found via search on
Google suggests that on-store apps will be found by abusers.
The dual-use nature of most of these on-store apps suggests
that tools used for IPS are, and will continue to be, allowed
on app stores.
To gather actual examples of off-store apps (distributed
outside Google Play), we examined all references to apps
found in the 100 manually-analyzed URLs. We also found
479 domains (among the full set of 7,167 domains returned by
searches) containing the words “spy”, “track” or “keylog”. We
investigated a random subset of 50 such domains, and found
that either they are discussing or hosting spyware apps. Finally,
we came across a web service called AlternativeTo [11],
which gives suggestions for alternative apps for some queried
application. We queried this service with the apps we had
identified thus far to find more spyware apps.
Ultimately we found 32 unique off-store apps. These all
constitute overt spyware, as they advertise their ability to
surreptitiously track and monitor a device. Nine of the apps
had been discontinued at the time of our study and are no
longer available. The remaining 23 serve, in later sections, as
our corpus of off-store apps. We believe this corpus compre-
hensively represents a current snapshot of off-store spyware:
in many subsequent manual searches about IPS related topics
in the course of this research, we did not find any reference
to additional off-store spyware.
B. Searching for IPS-relevant apps in Google Play
Our results above revealed that apps on Google Play come
up when searching Google for IPS-related phrases. We there-
fore investigate Play Store directly, to see what types of IPS-
related tools it hosts.
We perform a similar query snowballing procedure as
discussed above using the query completion API provided
by Google Play with smaller seed queries (as opposed to
the longer ones used in the previous Google search, see
Appendix A). In Google Play search, the snowball querying
converged rapidly to a final set of suggested phrases.
With each phrase in the final set, we search Google Play
and collect the metadata of the first 50 apps returned. This
metadata contains, among other information, the description
of the app, the minimum version of Android supported by
the app, the date of the last update to the app in the Play
Store, a range for the number of downloads, the average user
rating, and a unique identifier (called the Android app ID). For
each application we also downloaded the most recent reviews
(up to 200, the API limit), and the requested permissions as
listed in the application’s manifest file. We did this search
using a modified version of an unofficial scraper for Google
Play called google-play-scraper [48]. We limit our searches to
at most five queries per second to minimize any operational
overhead on the search engines. This type of scraping is
generally considered acceptable research behavior [45].
Every day3for one month starting on Oct 23, 2017, we
repeat query snowballing, and then perform searches on the
cumulative set of queries found in earlier days.
Results. On average the size of the query snowball retrieved
each day was 530 (with a standard deviation of 6). The set of
queries retrieved every day changed over time even though the
seed queries were the same. Every week, we saw about 40 new
queries gathered using our snowballing approach. The total
size of our query pool was 675 after one month of crawling.
In Figure 3a we show the change in the number of terms we
saw via snowballing and the total size of the query pool each
day. Google updates their query completion API periodically
to incorporate recent searches by users, which might account
for the periodic increase in the cumulative set of terms even
after crawling for a month.
The number of apps found in this process also varies
over time — rather more rapidly than the queries. We found
an average of 4,205 unique apps each day (with standard
deviation 450). We saw on average 288 new apps each day,
with a similar number of apps going missing (ones found in
previous days not found via our search procedure on a given
day). See Figure 3b. In total we collected 9,224 apps.
Our measurement suggests that the results of searches
change significantly over time. Part of this is the change in
the set of queries searched, and the rest is due to the fact that
many apps are removed from Google Play, some are updated,
and new apps are posted. Looking at the update date, we found
that 32% of all 9,224 apps were updated at least once, and 15%
were updated three times during our one month of study. Every
week on average 15% of the apps’ binaries were updated, with
the highest number of apps being updated on Mondays and
Thursdays (see Figure 3c). We also found that 208 (2%) of
the observed apps were removed from the Google Play store
(the Google Play pages of these apps return HTTP error 404)
during our study period. Apps may have been removed by
Google or by the developer, though we do not know which is
the case for these apps.
Developers can classify their apps within a fixed set of
genres, which improves discovery of the app. However, we
found inconsistencies in the reported genres of some apps. For
example, an IPS-relevant app titled Friends & Family Tracker
was listed as a casual gaming app.
Among the 9,224 searched apps, many were not relevant to
our study. For example, the search results include many apps
for tracking finances or pregnancy, which cannot be used as
spyware. This necessitated a mechanism for pruning apps that
are not IPS-relevant.
3Scans were not performed on Nov 07 and Nov 08 due to a power failure.
5
10-22 10-27 11-01 11-06 11-11 11-16 11-21
550
600
650
700
Date of crawl (mm-dd)
# of phrases
Cumulative
Daily
(a)
10-22 10-27 11-01 11-06 11-11 11-16 11-21
4,000
6,000
8,000
Date of crawl (mm-dd)
# of apps
Cumulative
Daily
(b)
10-22 10-27 11-01 11-06 11-11 11-16 11-21
100
200
300
400
Date of update (mm-dd)
# of apps
Apps updated
(c)
Fig. 3: (a) The size of Google Play recommendation snowballs each day, and the size of the cumulative set of distinct queries. (b) The
number of distinct apps found each day, and the cumulative number of apps over time. (c) Number of apps updated each day by the developer.
C. Pruning false positives
Many of the apps we discovered via Play Store search are
not relevant to IPS, as per our scoping discussed in Section II.
We therefore need to filter out such false positives. The large
number of apps suggests the need for a scalable approach.
Pruning via machine learning. We decide to use supervised
machine learning to help filter out apps that are not IPS-
relevant. We hand labeled 1,000 randomly sampled apps from
the 3,777 apps we found in the first day of crawling (ignoring
the apps whose descriptions are not in English); we refer to
this dataset as TR. We labeled them as IPS tools or benign
based on the information available on their Google Play page.
Of these 1,000 apps 280 (28%) were marked as IPS tools.
In building the model, we consider the description, sum-
mary, genre, and list of required permissions of the apps. We
tried other information, such as installation count and reviews,
but did not find any improvement in accuracy.
We used a bag-of-words (BoW) model for the descriptions
and summaries using the CountVectorizer function provided
by the Scikit-Learn [50] library. We considered n-grams of
words, for 1n4to construct the BoW model, ignoring
those that appear in less than 1% of the apps or more than
95% of the apps. From the BoW model we picked the 1,000
most discriminatory features based on the χ2-statistic [61]. We
treated each permission and each genre as individual words,
and created a BoW model for them. We picked the 50 most
discriminatory features from this model based on χ2-statistic.
Finally, we took the union of these features to represent each
app in a 1,050-dimensional feature space.
To train our model, we tried different machine learning
approaches, which we compared using an area under the
curve (AUC) metric [33]. For each ML algorithm, we perform
10-fold cross validation with randomly selected folds using
the hand-labeled training data TR, and then considered the
average value of AUC across all folds. We used Python Scikit-
Learn [50] to train and evaluate machine learning models.
We found that logistic regression (LR) with L2penalty and
inverse of the regularization strength (C) set to 0.02094 (found
via grid search) worked the best, giving an AUC value of 0.94
(optimal value is 1.0). This leads to a false positive rate (FPR)
of 4% and a false negative rate (FNR) of 4%. We tested, among
Threshold TR TS1TS2TS1+2
0.5
Accuracy 96 91 95 93
FNR 4 4 10 6
FPR 4 11 6 9
0.3
Accuracy 86 82 81 82
FNR <10 0 0
FPR 19 25 24 25
Fig. 4: Performance (in percent) of LR classifier on training
and different test sets for two classification thresholds.
other algorithms, decision trees, random forests, K-means, and
SVM, and found none performed better than LR.
Evaluation. We finally evaluate our machine learning model
on 200 apps from two different time periods. Half of these apps
(denoted by TS1hereafter) are sampled from the first week’s
6,361 apps (omitting the first day’s results that were used to
select the 1,000 training apps) and the other half (denoted
by TS2) were sampled from the fourth (last) week’s 7,581
apps. We hand-label the 200 apps as benign or IPS-relevant
as before. TS1has 28 IPS-relevant apps, while TS2has 22.
In Figure 4 (first group of rows, with cutoff 0.5) we note
the accuracy, FPR, and FNR of the logistic regression model
on the training data (TR) and the two test sets (TS1and TS2).
We see that the LR classifier generalizes well, as the test
accuracy is close to that of the training dataset. Moreover,
the model handles concept drift well: apps from a month later
are as accurately classified as those coming from the same
time period. Averaging across the entire test set (TS1+2), the
classifier achieves 93% accuracy with 6% false negatives.
We would like to minimize false negative rates — erro-
neously classifying an app usable for IPS as benign. Looking
ahead to potential use of our classifier as a detection tool,
failing to detect IPS apps on a phone is dangerous in many IPV
settings; while misclassifying benign apps creates overhead,
but is relatively harmless. We thus experimented with multiple
classification thresholds (how confident does the LR model
need to be before we classify something as IPS-relevant). We
found that a threshold of 0.3 (as opposed to a standard 0.5;
the positive class is IPS apps) achieves false negative rate
below 1% and false positive rate at 19%, with 34% of all
apps marked as relevant. These numbers are averages over 10
6
random folds of the training data. The performance at this
threshold on test data appears in Figure 4.
The false positive rate could be reduced via manual in-
spection of the ML-pruned apps. For example, in subsequent
sections we only investigate apps that we manually verified
to be IPS-relevant. Towards scaling manual inspection, we
explored using Amazon Mechanical Turk, see Appendix C.
D. Limitations of our app discovery approach
There are a few limitations to our app discovery approach.
First and foremost, we only focused on English-language
search queries and on apps with descriptions in English.
Therefore, some spyware used in non-English-speaking com-
munities may be missed. That said, our methods can readily
be localized to other languages.
Our initial seed queries are manually picked and the snow-
balls do not represent an exhaustive set of search terms that an
abuser might use. As a result, it could be that our techniques
missed some IPS apps.
Our machine learning and manual labeling approaches
primarily relied on descriptions on the Google Play store,
but some apps have only cursory, vague, or incomplete de-
scriptions. Some apps have capabilities not listed in their
description. Other apps promise capabilities they do not de-
liver. (In the next section we discuss some examples.) Many
of the apps falling into this category have more comprehen-
sive specifications on a separate website, and future work
might attempt to additionally leverage this information to
improve accuracy. Likewise, using natural language processing
techniques (e.g., [49]) might help in improving accuracy.
As another route to improvements, one might augment our
techniques with direct analysis of app binaries, perhaps using
the rich set of techniques that have been developed to analyze
(other kinds of) malware apps [14,24, 32, 44, 59].
Finally, what exactly should be considered IPS-relevant is
not always clear, even to expert human analysts. Our ground
truth labels may therefore contain some errors for apps on
the margin, and we tended to bias towards conservatively
marking apps as IPS-relevant, for the same reasons we tuned
our classifier towards a low false negative rate. This viewpoint
seems appropriate, given the many online resources we found
that suggest using truly well-intentioned apps (such as folder
synchronization tools) for IPS.
IV. IPS-RELEVANT APP UX AND CAPABILITIES
In Section III we discuss how we discovered IPS tools
through manual and automated crawling. Here we dig into
the types of apps found. We group them into various high
level categories, and then analyze both their user experience
(from the perspective of both abusers and victims) as well as
their capabilities.
App selection. We manually investigated 70 apps chosen
from our corpus of apps: 61 from Google Play (on-store),
and 9 from the open web (off-store). The apps were selected
as follows: We ordered on-store apps in decreasing order of
their download counts and chose apps until we had at least
three apps from each category (see Figure 5). We capped the
maximum number of on-store apps to consider for a category
to 15, ignoring apps with lower download counts. Of the 23
off-store apps we observed, 18 apps could be downloaded
without entering any credit-card information, whereas the
remaining 5 needed to be purchased. We randomly selected
6 of the free apps and 3 that required purchase.
For each app, a researcher reviewed the description of the
app, installed it on a simulated victim phone, installed any
complementary version on a simulated attacker phone (both
phones running Android 6.0), and recorded the capabilities
provided by the app. We found that 12 of the 70 apps were
buggy or did not work in accordance with their description;
they are excluded from the discussion below.
We observed that most apps fell into three categories based
on their intended usage.
Personal tracking: These are apps intended for use solely
by the owner of a phone. Examples include text message
forwarding services and anti-theft (Find-my-phone) apps.
Mutual tracking: These apps allow a group of people to
track each other’s locations. Examples include Find-my-
family apps, or couple trackers.4
Subordinate tracking: These apps are designed to enable
one party to track another, and not vice versa. Examples
include child or employee monitoring apps. Most off-store
IPS spyware falls into this category.
In Figure 5, we summarize these categories, with examples.
Some of the on-store apps that we investigated seemed,
in our assessment, to violate Play Store policy. We therefore
reported them to Google, who subsequently reviewed the apps
and took action against all those apps that they found to violate
their policy. These included some that lacked a persistent
notification or that promoted themselves as spyware or stealth
tracking (see discussion below).
A. (Ab)user experience
Assuming physical access to a victim’s unlocked device,
installation and configuration of most apps is straightforward.
Prior work [40, 58] reports that abusers often have access to
victims’ phones and either know, can guess, or can compel
disclosure of the credentials needed to unlock it.
Most of the apps we evaluated, both on and off Play
Store, have a subscription payment model with tiered pricing
for a range of capabilities. Some have free trials or free
versions with limited capabilities. The popular dual-use apps
(with more than 10 million downloads) on Play Store cost
somewhere between $5 for a lifetime upgrade (Wheres My
Droid) to $10 USD per month (TrackView). In contrast, the
apps that are distributed on the web range in cost from $20 to
$50 USD per month (for up to five phones).
On-store apps can be installed via the Play Store app on
the device. To install off-store apps, the abuser must first con-
figure the device to allow installation of apps from “unknown
4Couple trackers’ benign use case is for consensual location and information
sharing between partners, differentiating it from their dual-use in IPS.
7
App types Description Examples Capabilities
Personal
tracking
Find-my-phone Locate phone remotely Find my Android Location tracking, remote locking and wiping
Anti-theft Catch the phone thief Wheres My Droid Record location, photos & ambient audio; alert on SIM change
Call recorder Record incoming / outgoing calls Call Recorder Record calls and back them up to a server
Data syncing Sync data from phone to other device mySMS Sync SMS and call log, media, browser history
Phone control Control phone remotely TrackView Full control with capabilities exceeding combination of data
syncing and anti-theft
Mutual
tracking
Family tracking Track location of family members Family Tracker Mutual location sharing
Couple tracking Consensual sharing of location and more Couple Tracker Syncs location, media content, SMS and call logs
Friends tracking Track friends if they are in vicinity Friends Tracker Like family tracker, and alerts if friend in vicinity
Subordinate
tracking
Employee tracking Track employees whereabouts Where’s my Staff Similar to anti-theft
Parental control For parents to monitor their children MMGuardian Capabilities very similar to phone control
Overt spyware Claims to be spying app Cerberus, mSpy, HelloSpy Surreptitious phone monitoring & control
Fig. 5: Different categories of IPS-relevant apps and their typical capabilities.
sources” and disable Google Play Protect [4] regular scans.
The link to download the app’s APK is then found via browser
or sent in an SMS link. As mentioned in Section III, there are
many resources online that provide step-by-step instructions
on how to do this. Installation and configuration usually takes
only a few minutes of access to the victim’s phone.
Remote installation of dual-use apps is possible from the
Google Play web interface if the abuser knows the credentials
of the device’s primary Google account. However, Android
enforces that no third party apps — those not packaged with
the OS — can run until they are first opened on the device. The
abuser must also grant permissions (for GPS, SMS and call
logs, camera, and microphone, etc.) to either on or off-store
apps, otherwise Android will not allow the app to access this
information. Thus, for all apps we analyzed, an abuser needs
to have physical access to the device at least once to perform
activation. The exception here is when a dual-use app comes
packaged with the OS, such as a family tracker provided by
a smartphone manufacturer or cellular providers. We discuss
these special cases in Section IV-C.
Once the app is installed and the permissions are granted,
the abuser links the victim device to their credentials so they
can access it remotely. Credentials may be a username and
password, or a license number (for apps that require a paid
subscription). All of the off-store spyware we analyzed can
be configured to hide the app icon from the app drawer. Two
of the 61 on-store apps we analyzed had this feature as well
(Cerberus and TrackView).
Depending on the type of IPS app, the abuser is able to
access gathered data in different ways. Most personal-use apps
simply forward data to an email or a phone number that the
abuser controls. Mutual trackers generally require installation
of the app on two phones, one used by the victim and one used
by the abuser. Some subordinate tracking apps also require a
complementary app, but the majority offer web portals for
accessing information from the target device. We discovered
that several portals have simple but severe vulnerabilities that
allow an arbitrary user of the spyware service to access sen-
sitive information taken from any victim phone, and not just
the ones associated with the abuser’s account. We repeatedly
attempted to disclose these vulnerabilities to the vendors, but
never received a response.
No app that we analyzed required rooting the victim’s
phone [7], which is a technically sophisticated process for
average users and is difficult using only software for Android
6.0 or above. That said, many off-store spyware apps offer
additional functionality should the device be rooted, most
notably the ability to read contents of messaging apps such
as WhatsApp (which can’t be done without root access).
Some companies (e.g., FlexiSpy) sell phones that have their
software pre-installed (with customized versions of Android or
phones already rooted or jailbroken), providing a streamlined
abuser experience with the most invasive monitoring abilities.
As abusers often purchase and pay for the phone used by
survivors [29], this is an acute threat. In summary, installation
and use of IPS apps is easy for abusers, and gives them
dangerous surveillance capabilities.
B. App Capabilities
Both on-store and off-store apps provide a shocking array
of capabilities ranging from simple location tracking to near-
complete remote control over a phone. We separate our
discussion into three dimensions: monitoring abilities (what
information is being extracted), covertness, and control.
Monitoring abilities. Most fundamental to IPS is an app’s
ability to monitor a victim’s device. IPS apps typically gather a
subset of the following types of information: location, commu-
nication logs (SMS and call logs), communication data (SMS
content or call recordings), media content (photos, videos, or
other files stored on the device), and phone usage (app usage
or web history). In addition to passively gathering information,
many apps can take photos or record ambient sounds in real
time in response to an abuser’s remote command.
Most basic dual-use apps are GPS tracking apps that record
the location of the device and sync it with a remote server.
A user can log into the remote portal to locate the device.
Some dual-use apps, such as family locator apps, allow sharing
this location data, and therefore enable mutual tracking among
family members or friends. Most versions of Android and iOS
ship with a built-in find-my-phone functionality; we discuss
these apps in Section IV-C. Many third party find-my-phone
apps, such as Find My Android, dispense with a remote server;
8
instead they are triggered by an SMS with a code-word and
respond via SMS with the device’s location.
Anti-theft apps, built to recover stolen phones, provide
functionality beyond location tracking. For example, Wheres
My Droid can take photos, record ambient audio, and wipe or
lock the device remotely in stealth mode. It sends a notification
if the SIM card is changed, sends full call and SMS logs,
and sends GPS location of the phone if it is low on battery.
Cerberus, another app built for anti-theft, provides all that
functionality, along with a remote Android shell in its web
portal. This means almost anything that can be done while
using the phone can be done remotely. As previously dis-
cussed, Cerberus is recommended for IPS in blogs and forums.
Similarly, survivors and professionals working with them have
indicated that anti-theft apps are used in IPS [23, 29, 53].
Basic data syncing apps synchronize information across
devices. A common personal use example is SMS forwarding
with apps such as Mysms, which in an IPS context allows
an abuser to monitor text messages. There are other file
synchronization apps that will automatically copy one or
more configurable folders (set during installation) to a cloud
location. While these may seem benign, at least one IPS-
related forum we found suggests using such an app in con-
junction with a call recording app (that automatically records
all incoming and outgoing calls) to listen in on a victim’s
communications.
Couple tracking apps are designed for mutual tracking, and
tend to provide both location and data syncing. For example,
Couple Tracker, which must be configured on a pair of phones,
automatically shares with the other party location history, call
logs, the first 30 characters of every sent and received SMS,
and even Facebook activity (if provided with the credentials).
Phone control and child monitoring apps often provide some
of the richest capabilities. Phone control apps are built for a
user to remotely control their own phone for convenience,
while parental control apps are meant for parents to keep
an eye on their child’s phone activity. Both types of apps
provide access to location, SMS contents, call logs (sometimes
recordings), all media contents, app usage, Internet activity
logs, and even keylogging. Some apps can be configured
to send notifications when the monitored phone engages in
certain activities, like leaving a set geofence or calling a
specific number. We note that all of the off-store spyware
apps that we analyzed describe child safety as one of their
use cases. An off-store app called TeenSafe (not found in our
abuser-oriented searches), makes it difficult to use for IPS by
checking the age of the Google account to which the device
is registered. Abusers complain in reviews of TeenSafe about
the difficulty in using it for IPS.
Covertness. In an IPS context, it’s beneficial to an abuser if
tools are covert, meaning they can operate without the victim’s
knowledge, and can potentially remain undiscovered even if
the victim looks through all the apps in their app menu. Here
we examine how difficult it would be for a victim, assumed to
be of average technical sophistication, to notice the IPS app.
In Section VI we discuss software tools for detecting spyware.
The Google Play developer policy obligates apps to “Present
users with a persistent notification and unique icon that clearly
identifies the app” [1] whenever the app is collecting sensitive
information. Certain notifications are enforced by the operating
system, such as the GPS usage notification icon that appears
in the dock at the top of the screen whenever an app is using
location service. This icon does not specify which app is
using GPS, and is ever-present for many Android users. Other
notifications are not OS-required, for example we encountered
apps that by default do not display any notification when using
the camera or microphone.
Even when notifications are present, we suspect victims are
unlikely to observe them, let alone properly interpret their
meaning. Prior work has shown how poorly users respond
to other types of security indicators (e.g., the TLS lock in
browsers [13, 52]).
Almost all off-store apps and even some on-store apps
can be configured to hide their icons. (The OS does not
enforce that an icon be displayed.) One off-store example
is iKeyMonitor, which allows icon hiding, and can be later
accessed by dialing #8888B(an abuser can set the secret).
An on-store app called TrackView leaves no access point on
the device once the icon is hidden, but allows all of the app’s
settings to be changed from an app on the abuser’s phone.
Cerberus is another on-store app that hides its icon.
Control. Some spyware apps allow an abuser to remotely
control the device. Child safety apps can be configured to
block specific apps, impose browser restrictions, or limit the
number of hours the phone can be used in a day. Anti-theft
apps allow remotely locking the phone or wiping all data from
the phone. Some apps, broadly classified as phone control
apps, allow the abuser to remotely change the phone’s settings,
such as (re-)enabling GPS or WiFi.
Apps that allow such control of a device rely on commands
being sent either through the customer’s web portal (and
thereby the company’s server, which then relays the command
to the device) or by sending an SMS to the phone containing
a keyword that triggers a response from the app (the spyware
passively observes all incoming SMS). Most of these apps
allow the customer to customize their SMS keywords and may
even hide the SMS from view in the UI.
C. Bundled dual-use apps
An important class of dual-use apps that fall outside the
dichotomy of on- or off-store apps are the tools packaged
with the OS, either by a cellphone manufacturer or a cellular
service provider. One example of the latter is the Verizon
Family Locator. These do not require an abuser to install an
app on the phone, and often can be remotely activated with
the credentials attached to the account that pays the cellular
bill. Android natively provides tracking functionality, via Find
My Device, or via Google Maps’ unlimited location sharing
functionality. Assuming the abuser has access to the victim’s
Google credentials, the abuser can remotely turn on the Google
9
Maps Timeline feature and obtain periodic (even historical)
information about the victim’s location. Google Drive and
iCloud provide data syncing functionality to the cloud, and
could be abused for extracting data from the device.
Some bundled apps that we investigated show notifications
to the current user of the device. For example, Find My
Device sends a notification stating that your device is being
tracked. Adding a member (in an abuse context, the victim)
in the Sprint Family Locator will send an activation SMS
to the victim’s phone. Even in these cases, as mentioned,
notifications can be ignored or suppressed should the attacker
have temporary physical access to the device.
These apps can be impossible to uninstall as they are bun-
dled with the OS; at best they can be disabled. Looking ahead
to mitigation, these apps will require different approaches than
that used for on-store or off-store apps. See the discussion in
Section VII.
V. E VIDENCE OF DEVELOPERS’ CO MP LI CI TY
In this section, we investigate the use of dual-use apps for
IPS. The makers of some of these apps are not only aware
of such abuse but are actively supporting the IPS use case
via advertisement, by failing to refuse a potential customer
that wants to use their software illegally, or failing to help an
ostensible IPS victim being monitored by their software.
A. User Comments
On Google Play users can leave reviews of apps they have
downloaded. We collected 464,625 reviews from over 9,000
apps. We searched for reviews mentioning both an intimate
partner (husband, wife, boyfriend, bf, gf) and an IPS action
word (track, spy, cheat, catch), and manually analyzed the
results. We found 103 reviews on 82 apps that explicitly
mention that the app is used for tracking or spying on a current
or previous intimate partner. For example, a comment left for
SMS Tracker Plus, an app which claims to be for parental
control, states: “Love it!!! I’ve been suspecting my gf cheating
and this gave me answers really quick kick the curb girl”. Another
comment on ATTI Shadow Tracker, an app which markets
itself for tracking a fleet of long-haul truckers, states: “Love it!
I can now keep an eye on my possibly cheating wife!”. While we
cannot verify the content of these reviews, we have no reason
to suspect that they are dishonest.
B. Advertising
We found that many IPS apps, including dual-use ones,
advertise IPS use cases directly or indirectly.
Google search advertisements. We searched Google with a
subset of 1,400 queries from the 10,000 terms we found in
Section III-A and recorded the ads shown on the first page
of the search results. We found thousands of ads shown for
search terms that show explicit intention of IPS, e.g., “how
to catch a cheating spouse with his cell phone”. A detailed
analysis of advertisements shown on Google searches is given
in Appendix D.
The ad texts often indicates that companies are advertising
IPS as a use case. An ad recorded on March 10th 2017 for
mSpy says “Catch Cheater with mSpy App for Phones. Invisible
Mode. Track SMS Chats Calls Location & Other. 1.000.000+ Satisfied
Users. Try Now!” Another ad recorded the same day for
FoneMonitor reads “Track My Wife’s Phone — Want to Spy on
your Wife? Track your Wife without her knowing. Discover Who Are
They messaging. Download! 24-Hour Support Price Superiority No
Jailbreaking and App Results Guaranteed.
We informed Google about the IPS search terms that showed
ads during our experiment. In response, Google expanded their
restriction of ad serving on those types of search terms. We
confirmed that ads are not being shown on explicit IPS search
terms at the time of the final version of the paper.
Play Store. The Google Play website does not serve adver-
tisements, but the Play Store app does. We chose some of the
malicious terms from the snowball set and did manual searches
in the Play Store app on an Android device. We found that
apps on Play Store were also advertising on search terms like
“phone spy on husband” or “see who bf is texting without
him knowing.” While a more systematic study is needed, it is
clear that apps are being (and are allowed to be) advertised for
IPS-related searches. After we shared the result of our study,
Play Store has also expanded their restriction of ad serving on
those types of search terms.
Blogs as IPS advertising. As mentioned in Section III-A, we
found that Google searches such as “how can I read my wife’s
texts” yielded many blogs and forums providing advice. Some
of these “blogs” were hosted on the domain of a dual-use app
and explicitly outline why their product is ideal for covert
tracking, sometimes accompanied by imagery of a battered
woman and verbiage such as “men need to have control of their
families”. An egregious example appears in Figure 1. These
pages then link back to the site of the app, which is hosted at
the same domain but in some cases have a completely different
page format.
In addition to such advertising sites that appear on the same
domain as an app’s, we identified many ostensibly unaffiliated
websites, blogs, and forums that serve the sole purpose of
directing those interested in conducting IPS to a specific dual-
use app. As one example, catchthemtoday.com, a blog focused
on IPS has content such as “Don’t Be A Sucker Track Your
Girlfriend’s iPhone Now: Get It Here: Catch Her Today”. The last
three words are a Bitly link to appitunes.blogspot.com, which
automatically redirects to mSpy.com. The blogspot.com page
claims to have been last updated in October, 2017. It includes
text that mSpy was created for child safety and employee
monitoring uses, and that “mSpy is not liable for other ways
of the software use”. (The redirect, however, ensures that this
disclaimer is never seen.) The mSpy webpage, though, only
discusses the child safety and employee monitoring use cases.
Direct marketing. During our manual analysis of apps
in Section IV, we created accounts with, but had not yet
purchased subscriptions for, several of the companies whose
10
customer service departments we later engaged (see below).
We found that our dummy account received marketing emails
encouraging us to sign up for their services once our free
trials had expired. Two companies encouraged us to buy a
smartphone from them which would come prepackaged with
their software (for streamlined abuser experience). We saw
comparable advertisements for iOS. While these emails don’t
explicitly suggest giving these devices to an intimate partner,
these same companies do advertise those use cases elsewhere.
C. Customer Support
Though some companies actively advertise IPS as a use
case, we suspected that many more turn a blind eye to it. To
investigate this, we contacted customer service departments
posing both as an abuser and a survivor to see how they
responded. Our IRB confirmed that this is exempted from
review, as the interaction is in their professional capacities
and does not collect any PII. We selected a subset of 12 apps,
5 off-store and 7 on-store. We chose a set of apps that had
shown advertisements on IPS-related terms, or that we knew
to be widely used, either by install counts for on-store apps
or by blog and forum mentions for off-store apps.
To investigate the attitude of a company towards the use
of their software for IPS, we initiated live chats or email
conversations with their customer support teams, posing as
a potential abuser. Only 11 of the 12 apps offered any way to
contact them.
All conversations were initiated from a Gmail account
associated with the name Jessica and began with the following
prompt:
Hi, If I use this app to track my husband will he know
that I am tracking him? Thanks, Jessie
If customer service responded to this prompt with a question,
such as “What kind of phone does he have?” we continued
the conversation in an attempt to elicit the company’s attitude
towards this use case.
Of the 11 companies we contacted, 2 have yet to respond.
Of the 9 that responded, one, TeenSafe, which is an off-store
app, delivered a strong admonishment and legal warning about
IPS. The other 8 responded with some version of “No, he
shouldn’t be able to tell”, making them complicit in potential
abuse. The customer support representative for TrackView,
which is available on Play Store and has an entire Google
Groups Forum for customer support, told us that with the paid
plan, the icon and all notifications could be hidden. We have
confirmed that this is true. TrackView is also the only company
that has responded to our inquiries posing as a survivor looking
for help removing their app. Their response showed no sign of
concern, and their advice of “look in the app menu and delete
it” was not useful, given that the app icon was concealed.
VI. IN EFFI CAC Y OF EX IS TI NG ANTI-SP YWAR E
The previous sections reveal the prevalence, ease-of-use,
and severity of overt spyware and dual-use apps. Moreover,
many of the tools are inherently, or can be configured to be,
difficult to detect by inspection of the device via the normal
UI. What can potential victims of spyware do? Current best
practice is circumstantial [30], with victims advised to suspect
spyware should there be spikes in bandwidth usage, decreased
battery life, slow responsiveness, or information the abuser
knows that is seemingly only possible to learn from spyware.
Typically, the only recourse for strong suspicions are factory
resetting or completely discarding the phone. Obviously it
would be better to have technical means for detecting and
mitigating spyware.
A number of tools do advertise the ability to detect and
remove spyware, perhaps suggesting defenses against spyware
are close at hand. These anti-spyware tools range from mobile
versions of well-known, commercial anti-virus systems such
as Avast, Norton, and ESET, down to barely functional apps
that appear to be scams. In this section we put these counter-
measures to the test to see whether they should be used by
potential victims.
A. Anti-Spyware Tools on Google Play
There are many apps in the Google Play store that claim to
be anti-spyware tools. To identify these apps we followed a
similar procedure to that used for discovering spyware, but this
time performing searches from a potential spyware victim’s
perspective. We began our query snowball with the terms
“anti spyware”, “remove phone tracker”, and “spyware re-
moval tool”, and conducted snowball querying using the query
completion API provided by Google Play (see Section III-B).
The eventual snowball size was 13, and upon search with
those terms, returned 147 apps that have more than 50,000
installations as reported by Google Play. Manual inspection of
the 147 apps revealed 40 to be relevant for removing spyware.
All of them advertise a free scanning facility, but some charge
money to remove apps.
Among these 40 apps 7 were from major antivirus vendors:
Avast, AVG, Avira, ESET, Kaspersky, McAfee, and Norton.
The remaining 33 apps are from other vendors, though note
that some of these have more than 100 million downloads.
In Figure 6 we show the 19 anti-spyware apps that were
downloaded at least 10 million times or came up in the top 10
results for searching “anti spyware” in Play Store, as recorded
in November 2017.
Interestingly many anti-virus apps provide find-my-phone,
anti-theft, or family safety functionality, making these poten-
tially dual-use. None are covert, but even so these anti-spyware
tools could hypothetically be used by abusers as dual-use apps.
Nevertheless we do not consider them as such, because their
primary functionality is not for spying (see Section II). More
pragmatically, they are not returned in response to abuser
search queries and we found no evidence online or in prior
work of their abuse in IPS settings.
Experimental setup. To evaluate the efficacy of the anti-
spyware apps in detecting dual-use apps, we installed 276
dual-use apps out of 280 identified via manual inspection as
described in Section III-B on a device running Android 6.0
(Marshmallow). Four could not be installed due to compatibil-
ity issues. We also installed 20 out of the 23 off-store spyware
11
Anti-spyware tool D/L
(mn)
On-store
(276)
Off-store
(20)
Benign
(100)
360 Security 100 2 80 0
Anti-virus Dr.Web 100 2 70 0
Avast Mobile Security1100 2 70 0
AVG Antivirus1,2100 2 70 0
DFNDR Security 100 2 85 0
Lookout Security 100 3 75 0
ALYac 10 2 70 0
Antivirus (TrustGo) 10 2 80 0
Antivirus (TrustLook) 10 2 70 0
Avira110 3 60 0
Kaspersky110 1 85 0
Malwarebytes210 3 85 0
McAfee Mobile1,210 2 90 0
ESET110 1 14 0
Norton Mobile1,210 13 70 2
Virus Cleaner210 2 75 0
Anti Spy Mobile2147 95 12
Incognito21 2 5 0
Anti Spy (skibapps)2<136 73 10
Others (average over 21 apps) 1 2 70 0
Virustotal (3+ AVs) N/A 7 100 3
1Apps from popular antivirus providers.
2Apps among top 10 search results in Play Store for “anti spyware”.
Fig. 6: True positive (third and fourth columns, higher is bet-
ter) and false positive (final column, lower is better) detection
rates (in percentages) of anti-spyware apps available in the
Play Store ordered by reported number of downloads (second
column). The final row reports on using Virustotal to flag an
app if at least three AV engines flag the app.
apps we collected outside the Google Play store. Again the
remaining three could not be installed due to compatibility
issues. Finally to measure false positive rates, we installed the
100 top-selling apps (in November 2017) from Google Play
that are not usable as spyware (manually verified).
For each anti-spyware app, we first install the app, allow
it to complete its scan of the device, record its results, and
then uninstall the anti-spyware app. The output format from
the anti-spyware apps varies and often does not provide a
report that can be exported programmatically, so we manually
transcribe the results. Some anti-spyware apps give binary
classification, while others provide multiple types of classi-
fications. For example, Norton Anti-Virus categorizes apps as
“ok”, “malware”, “medium privacy risk”, and “high privacy
risk”. Whenever an app offered classification more granular
than binary, we counted anything not marked “ok” as being
flagged as spyware.
Evaluation. Of the 40 anti-spyware apps, 37 are completely
ineffective against dual-use apps, flagging at most 3% of them.
Most of the anti-spyware apps flag more than 70% of the
off-store spyware apps. The performance results of the anti-
spyware apps are given in Figure 6.
The ones that detect the most spyware have higher false
positive rates. For example, Anti Spy Mobile catches more
than 47% of on-store IPS-relevant apps, but flags Chrome,
Play Store, and Amazon apps as risky. Further investigation
revealed that these anti-spyware apps simply mark any app
that uses certain permissions as risky.
0 10 20 30 40 50 60
0
0.2
0.4
0.6
0.8
1
# of AVs
Fraction of apps
Off-store spyware
On-store spyware
Top-100 apps
Fig. 7: Fraction of off-store spyware, on-store spyware, and
top-100 apps (benign, non-spyware apps) detected by the
indicated number of AV engines available in Virustotal.
All but one of the top-brand anti-virus providers (e.g., Avast,
AVG, Avira, ESET, McAfee, and Kaspersky) detect less than
3% of dual-use apps. Presumably this reflects their design
goals, which do not necessarily include detecting IPS spyware,
let alone dual-use apps. Indeed in non-IPV contexts marking
some of the dual-use apps as malicious would represent false
positives to their users.
B. Virustotal Analysis
We also evaluate whether Virustotal [57], an aggregator of
many anti-virus engines, can be used to identify IPS apps.
Virustotal hosts more than 60 anti-virus engines (AV engines),
and a large number of tools for static and dynamic analysis
of content. Access to the Virustotal API is free for non-
commercial use and takes as input an MD5 or SHA1 hash
of an app’s binary.
We had Virustotal evaluate the 280 on-store apps identified
in Section III-B as well as the 23 off-store apps. Figure 7 gives
the fraction of on-store and off-store IPS apps and the top 100
benign apps flagged by at least the indicated number of AV
engines. As one datapoint, only 21 apps out of 280 on-store
dual-use apps (8%) were flagged by at least three AV engines.
The best two AV engines were Cyren and WhiteArmor. Cyren
flagged 6% of the on-store IPS apps, and 70% of the off-
store spyware, but Cyren also flagged one of the top 100 apps
(Pandora Radio). WhiteArmor flagged less dual-use apps than
Cyren (only 5%), but flagged all of the off-store spyware, and
did not have any false positives. In the end, we conclude that
these engines are not designed to catch dual-use apps, their
focus instead being on other forms of malware.
VII. DISCUSSION: DEALING WITH IPS SPY WARE
Spyware used in IPV settings endangers the safety and
privacy of survivors. As our measurements suggest, spyware
takes on many forms, ranging from apps overtly designed
and advertised for IPS to dual-use tools with functionalities
easily repurposed for IPS. Existing anti-spyware tools do not
sufficiently detect dual-use apps.
Thus, we propose a multi-pronged strategy for combating
IPS apps and improving safety for survivors. A full investiga-
12
tion of our suggestions will require significant future work —
here we outline ideas and discuss looming hurdles.
Improved detection and removal. An urgently needed first
step is to improve detection of IPS apps. We envision building
upon our measurement framework from Section III-B to con-
struct a proof-of-concept blacklisting tool capable of detecting
potential IPS apps. Apps need to be collected and labeled on
an ongoing basis. An issue to be dealt with is ensuring the
robustness of our crawling and detection infrastructure in the
face of malicious developers seeking to avoid classification as
spyware. For example, our ML classifier may be vulnerable
to evasion attacks [36,41,42]. We hope that anti-virus vendors
will extend their commercial tools to deal with IPS spyware
and dual-use apps, perhaps using our techniques.
The deployment of detection and removal tools faces par-
ticular challenges in the IPV context, as using anti-spyware
or removing IPS apps may risk escalation from digital abuse
to physical violence (see [29,30,46]). This means deployment
may require multiple modalities, such as a covert or easily-
removed anti-spyware app, or even use of a USB-connected
laptop at shelters (or other places that victims may go to obtain
help) to scan the device. New guidelines for safety planning
when IPS apps are found will be needed, as removing them
may be too dangerous in the short term.
OS notifications and protections. We found many IPS apps,
including on-store apps, work in the background without
proper notification — even when sensitive data (i.e., camera,
microphone, chat messages, photos) is being relayed. Two IPS
apps also hide their icon in the app drawer. Though Google
Play’s developer policy explicitly prohibits this [1], there is no
OS-level enforcement.
We propose that mobile OS developers strengthen user
protections by enforcing the policies in their developer agree-
ments. Bundled dual-use apps, such as Google Maps or iCloud
should take special steps to regularly inform the user if they
are syncing any sensitive data with a remote server. Future
work would be needed to evaluate the efficacy of specific
notification policies, as users do not always notice indicators
like “recording lights” [27, 51]. OS-level protections would
need to be carefully designed, so as not to be bypassable, at
least should the device not be rooted (c.f., [15]). Finally, and
most critically, these mechanisms would need to be carefully
constructed to balance the needs of legitimate applications of
dual-use apps with the threat of their use as spyware.
IPS use case prevention. Our measurements revealed that
dual-use apps are often advertised for IPS, both in paid
advertising channels and in organic marketing (e.g., blog posts
and search results). Some developers explicitly condone IPS,
while in other cases they do little to prevent it. We believe ad
networks, OS vendors, and developers can work together to
better prevent use of legitimate dual-use apps for IPS.
As a start, advertising networks should stop accepting paid
ads for search terms related to IPS/IPV. There is precedence
for this in other contexts, such as prescription drug advertis-
ing [55]. In response to this paper, Google has already stopped
showing advertisements on IPS-related search terms. Search
engines could also potentially preference information about
legality in response to abuse-related queries, hopefully creating
a deterrent for an abuser. Organic marketing will be difficult to
curb from a technology perspective, but here law enforcement
agencies, such as the FTC and DOJ in the United States,
might escalate their enforcement of policies against products
intended for illegal use, such as in the CyberSpy case [20,47].
Future work could develop guidelines for building apps
which are less attractive for IPS use cases. As an example,
parental control apps need not be surreptitious, so they could
be made conspicuous. Similarly, SMS syncing apps should
always show clear notifications when forwarding to another
device, as done by some messenger apps already [31]. Finally,
developers could better monitor comments and reviews, and
refuse to continue service to people indicating an IPS usage.
For example, TeenSafe’s customer service refused to help us
when we indicated we intended to use their app for IPS.
VIII. CONCLUSION
In this paper we provided the first in-depth measurement
study of the ecosystem of software used for IPS on mobile
devices. Taking the view of an abuser, we used manual
as well as automated crawling to document the abundant
resources currently available to abusers, including how-to
guides, question-and-answer forums, and apps. Over a one
month period, we crawled the Google Play Store and used
a combination of manual review and machine learning to
discover a large amount of dual-use apps: those designed
for some legitimate use, but which are being repurposed by
abusers for IPS. By investigating advertising behavior, online
forum discussions, and customer service responses, we showed
that many dual-use app vendors are tacitly facilitating or,
in some cases, condoning IPS. We measured the efficacy of
existing anti-spyware tools and found them insufficient for use
in IPV contexts.
Given that abusers use IPS apps to cause emotional and
physical harm, including even murder, there is an acute need
for the security community to help mitigate the threat. In
response to our paper, Google improved safety for their users
by taking action against apps that violated Play Store policies.
They have also increased restrictions on advertisement serving
for IPV-related queries. More broadly, we have initiated dis-
cussion about future work ranging from improved detection
tools to legal and regulatory improvements. We hope future
research and advocacy will further increase digital security
and safety for those suffering in IPV situations.
IX. ACKNOWLEDGMENTS
We thank Kurt Thomas and others at Google for their feed-
back, as well as the anonymous reviewers for their insightful
comments. This work was supported in part by NSF grants
1619620, 1717062, 1330308, 1253870, and 1514163, as well
as gifts from Comcast, Google, and Microsoft.
13
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APPENDIX
A. Query snowballing, seed queries, and initial filtering
We use a query snowballing technique to find a com-
prehensive set of search terms using the recommendation
APIs provided by search engines. In Figure 8, we give the
pseudocode of our snowballing approach. The algorithm takes
as input a set of seed queries and the maximum number of
queries to return. We use different seed queries for Google
and Google Play, because of the different nature of the query
recommendation APIs. While the former suggests semantically
related queries, the latter provides only query completion. The
initial seed queries for both searches are listed in Figure 9.
Both the recommendation APIs return lots of unrelated
search terms, more so in Google than in Google Play. For
example, “cheating” is expanded to a game “cheating tom”, or
“cheating husband” is expanded to “cheating husband quotes”,
none of which is what we are looking for. As we expand
the search results repeatedly, unrelated queries will drive the
snowball away from related terms. We therefore filter the
QSnowball(Qinit,`):
Qφ
while |Qinit|>0do
qpop(Qinit);QQ∪ {q}
If |Q| ≥ `then return Q
Yrecommend(q)
Y0filter(Y)\Q
Qinit Qinit Y0
return Q
Fig. 8: Query snowballing approach. Here recommend represents
a query recommendation API that takes as input a query string
and returns a set of recommended queries and filter uses regular
expression heuristics to remove unrelated search phrases. The set
Qinit is an initial set of query phrases and `is the limit of the size
on the query snowball Q.
suggested queries that contain any of the words (regular
expressions) listed in Figure 9 (right table).
B. IPS apps in iTunes App Store
During our Google search in Section III, we found several
dual-use apps enlisted on the Apple’s app store. All the off-
store apps that we found support both Android and iOS
platforms. To seek further evidence of IPS apps, we decided
to apply our measurement pipeline to the iOS platform us-
ing our crawling pipeline from Section III with only a few
modifications, as we discuss bellow.
Interestingly, unlike Play Store API, the search API pro-
vided by iTunes App Store (official market place for Apple,
also called App Store) does not return any search results or
query suggestions on many IPS relevant search terms such as
“catch your spouse cheating.” However, Google’s site-specific
search (searching by adding a prefix: “site: itunes.apple.com”
to the search term) returned several links to apps listed in
the App Store that are not found via direct search in iTunes.5
Also, we found iTunes query completion API returns a lot of
completely unrelated queries not relevant to IPS. We therefore
chose to use the snowball of search terms obtained using
Google Play store search suggestions to search iTunes and
Google for dual-use iOS apps.
Together via the direct search on iTunes and via site-specific
search in Google, we found 2,724 apps. Manual investigation
of descriptions of a random sample of 500 apps from this list
revealed that 97 apps (20%) are capable of IPS. The fraction
of on-store IPS apps we found in Apple is less than what we
saw for Android (28%). Among the on-store dual-use apps
enlisted in Google Play we found 9 IPS relevant apps listed
in iTunes App Store too (with very similar app identifiers).
However, many cross-listed apps have different functionalities
in iOS due to its more restricted permission model and
stricter enforcement of developer policy. For example, the
TrackView app in iOS does not hide their app icon or use the
camera surreptitiously, while in Android it does (as discussed
in Section IV-B).
5We tried similar site-specific search to find Play Store apps too (by adding
“site: paly.google.com”), but did not find any new app other than those we
already found via direct search in Play Store.
15
Google Play Google Blacklist
cheater, cheating, cheating {agent}, catch cheating, catch
cheating {agent}, catch {agent}cheating, track loca-
tion, track {agent}, family tracker, {agent}tracker, track
{agent}cheating, track {agent}phone, track phone, app
for tracking location, find my phone, find my lost phone,
find phone location, track my phone, call record, listen to
call, gps tracking, read emails from {agent}’s phone, spy my
{agent}, app for spying, apps for spying on my {agent}, spy
on my {agent}, track sms, sms tracker, sync sms, read sms
from another phone, message sync, phone control, control
kids phone, track email, track messages, track calls, hidden
keylogger, keylogger, keylogger for android, phone sync
how to catch my cheating {agent}app, how to track
my cheating {agent}app, app for spying on my
{agent}, app for tracking my {agent}, get location of
another phone app, listen to calls from another device
app, track my {agent}, track my {agent}s phone
without them knowing, track location of my {agent}
app, read sms from another phone app, app for tracking
my kids, app for seeing my kids phone, keylogger for
android, easy spy app for android, hidden spy app for
android, app to see photos in my phone remotely, see
all whatsapp messages app, see all facebook messages
app, spyware for android devices, record calls app
game, sport, mile, gta, xbox, royale, golf, fit,
food, flight, run, tracks$, car, cheating tom,
cheat.*code, refund, cheatsheet, chart, cheat.*sheet,
cheat.*engine, gas budd?y, calorie, money, ex-
pense, spending, tax, budget, period, diet, preg-
nancy, fertility, weight, gym, water, work ?out,
track and field, exercise, cheats, baby.*photos,
tv, time, hour, minute, day, month, year, sale,
ski, sleep, walking, block, anti.*tracking, rent,
nutrition, corporate, insta(gram)?, facebook, twit-
ter, tinder, spyfall, forms?, exam, dhl, fedex, ups,
read.*loud, quotes, ps4, ps3
Fig. 9: List of seed search terms (separated by “,”) for conducting query snowballing with Google Play and Google search.
Here {agent}is replaced with each of {boyfriend, girlfriend, wife, husband, spouse, partner}. On the right is the blacklist of
words or regular expressions used to filter queries that have them.
App Store does not provide all the information we get from
Play Store. Notably, in the App Store, permissions requested
by an app are not available. Therefore we had to modify and
retrain our machine learning algorithm separately for Apple.
For training and cross-validation we used the 500 hand labeled
apps mentioned above. The feature set was constructed using
the app description, the app title, and the genres of that app
as listed in the App Store. A bag-of-word model with pruning
was constructed in the same way described in Section III-C.
From the BoW model we pick the 1,100 most discriminatory
features (1,000 from description and 100 from the title and
the genres) based on χ2-statistic [61].
In 10-fold cross validation using logistic regression (LR)
model (with L2penalty, and inverse of regularization strength,
C, set to 0.0385), we found the classifier can accurately
classify 92% of apps, with a false positive rate of 7% and
false negative rate of 8%. If we set the cutoff to 0.3 (as we
did in case of Android), the false negative rate goes below 1%
with 10% false positive.
C. Pruning with MTurk.
In Page 6 we show how we can tune machine learning to
remove apps that are obviously irrelevant to IPS, leaving us
with nearly 34% of all apps that ML classifier flags as “dual-
use.” However, among the apps flagged by the classifier, nearly
20% are falsely tagged (based on our hand-labeled training
data). Therefore, we decide to use a second level pruning
of false positive apps from the Google Play store leveraging
Amazon’s Mechanical Turk (MTurk) to rapidly employ a large
pool of human workers to label apps as dual-use or not.
While our initial experiment does not produce results better
than the ML classifier, it definitely testifies the possibility
and opens up an interesting question of how to utilize a
crowdsourcing framework to perform a non-trivial task such
as identifying spyware apps based on their descriptions.
Pilot study to ensure feasibility. Though MTurk provides
an efficient method for simple classification tasks, such as
image tagging, our task is more nuanced, and could require
domain knowledge from the workers to perform correctly.
For example, the definition of a dual-use app is not always
immediately apparent, and often relies on “what-if” judgments
Ground Truth
dual-use benign Total
MTurk dual-use 30 1 31
benign 3 65 68
Total 33 66 99
Fig. 10: Confusion matrix of MTurk labels (majority among
5 workers) and ground truth (researchers’ labels) of 99 apps
(randomly sampled from TR) from the pilot study.
about potential app usage rather than any observable phenom-
ena. In order to verify MTurk’s viability for completing our
classification task, we conducted a pilot study with a small set
of workers.
As part of our required qualification test, we gave workers
a short (i.e., a couple paragraphs) description of dual-use apps
and examples of both benign and dual-use apps, including
some “borderline” cases. We then asked workers to classify
ten sample apps we hand-labeled beforehand as either benign
or dual-use. We found that most workers (84.6%) were able
to accurately classify all ten apps by their second attempt at
the qualification test.
Once a worker passes the qualification test, the worker is
allowed to accept actual classification tasks (HITs). Each task
contains 3 apps (with a $0.06 reward for labeling each app) and
must be completed by five different workers. For each app, we
take the majority vote of the classification submitted from all
five workers. To evaluate the promise of crowdsourced labels,
we first performed a pilot study by submitting 99 randomly
sampled apps from the TR set (data that we hand-labeled and
used for training the ML classifier). We use Cohen’s Kappa (κ)
statistic [19] to compare the agreement between crowdsourced
labels and the researcher-assigned labels.
In the pilot study, we found a promising agreement rate
between the crowdsourced labels and the researchers’ labels
(κ= 0.96; the maximum possible value of κis 1). This
amounts to 95% of the labels matching across the 99 apps, and
only a 1% false negative rate (taking the researchers’ labels as
the ground truth). In Figure 10 we note the confusion matrix
of this experiment. The results suggest the viability of using
crowdsourcing to identify dual-use apps.
Study with all the hand-labeled apps. Following the pilot
16
study, we submitted all of the remaining apps from our hand-
labeled set of 1,200 apps (TR +TS1+TS2) to MTurk. To
expedite the data collection, we included 7 apps in each HIT
for a total payment of 0.42 ($0.06 ×7) per assignment. All
of the apps were labeled by five different workers within 48
hours. However, the final agreement rate was worse than the
pilot study at κ= 0.64: only 85% of crowdsourced labels
matched the researcher labels, with a 12% false negative rate.
We found that a small number of the workers mislabeled
a relatively large number of apps. After removing all labels
from workers with agreement rate κ0.5, we re-submitted
the apps requiring more labels (using the same HIT format: 7
apps per HIT). We also modified our initial qualification test
by giving more exemplary instruction of major classes of dual-
use apps. After obtaining the new labeling the agreement of the
MTurk majority with the ground truth improved to κ= 0.76.
In Figure 11 we show the performance of the MTurk majority
labeling.
Evaluation. To conjunct MTurk into our rest of the pipeline,
we decided to use 0.3 as our classification threshold. With
this threshold, we do not submit any negatively-labeled apps
by our machine classifier to MTurk, and also the apps on
which machine classifier’s confidence is high (0.7). We only
submit the positive-apps for which the classifier’s confidence
is low (0.7). For the rest of the apps, we will take the ML
classifier’s labeling as the final label.
The final performance of this pipeline is recorded in the
Figure 11 (last row). Interestingly, the pipeline has consis-
tently lower false negatives across all datasets than logistic
regression with cutoff 0.5, while having similar false positive
rate. Also, we found for test data TS2, the accuracy is >97%,
better than the best machine learning can achieve.
While the initial results are not very promising, we can
improve on this. For example, given that the labeling dual-use
apps require some domain knowledge, we can design a more
nuanced worker-training process. Also, we can task workers to
identify capabilities and purpose of the apps, instead of making
a judgment call about whether or not the app is IPS relevant.
For example, the worker finds out from the description whether
the app can sync SMS, or can be used for parental control,
etc. This information can be used to further classify those apps
more accurately into IPS and benign categories. We leave a
detailed analysis of this approach as future work.
D. Analysis of Google Ads on IPS search terms
We searched Google for ten days in October 2017 with a
subset of 1,400 queries from the 10,000 terms we found in
Section III-A. We searched from a Chrome browser on an
OSX machine and recorded the contents of the first page of
the search results. We did not set up any user profile, and
performed each search from a new browser session (though
persistent cookies were not purged). We extracted a total of
7,776 ad impressions associated with 214 domains. Among
our search terms, 340 showed at least one ad during the
measurement period. The term “how to catch a cheating
Training Test
(1st wk)
Test
(4th wk)
dual-use 280 28 22
benign 720 72 78
Logistic
Regression
(cutoff: 0.5)
Accu. 96% 91% 95%
FNR 4% 4% 10%
FPR 4% 11% 6%
Logistic
Regression
(cutoff: 0.4)
Accu. 93% 88% 88%
FNR 2% 4% 10%
FPR 9% 15% 12%
Logistic
Regression
(cutoff: 0.3)
Accu. 86% 82% 81%
FNR <1% 0% 0%
FPR 19% 25% 24%
MTurk
(majority
among 5)
Accu. 91% 89% 96%
FNR 20% 11% 19%
FPR 4% 11% 0%
Whole
Pipeline
Accu. 96% 91% 97%
FNR 4% 0% 5%
FPR 5% 12% 3%
Fig. 11: Training and testing accuracy of our pipeline. First
two rows show the statistic of our hand-labeled data (ground-
truth). For the pipeline, we consider an app dual-use if LR
classifier’s confidence is more than 0.7 or if the confidence is
within [0.3, 0.7] and majority of MTurk worker labeled it as
‘dual-use’.
spouse with his cell phone,” served the most ad impressions
associated to 18 different domains. The most common domain
(truthfinder.com) appeared in 897 ad impressions across 112
different search terms.
We repeated the scraping process in November for three
days, following the publication of an article by The Daily
Beast accusing Google of showing ads about illegal spy-
ware [21]. We observed a total of 2,866 ad impressions
linking to 186 domains, resulting from 432 search terms. Some
searches yielded as many as 7 ad impressions on the first page
of search results. The most advertised domain remained the
same. We ran one further scrape in March for one day and
collected 1,843 ad impressions linked to 137 domains and 372
search terms.
We analyzed all 96 domains that appeared in at least 10
ad impressions across all measurement periods. These 96
domains are associated with 11,831 ad impressions (95%). Of
these domains, 20 belong to services offering public record or
reverse phone number lookups. Those represent half (6,217) of
the ad impressions. Another 22 domains are of tracking apps
and software and account for 3,128 ad impressions. Eighteen
domains (linked to 1,162 ads) belong to miscellaneous but
relevant sites, including: manufacturers of physical tracking
beacons, private eye services, blogs and forums of the kind
discussed below, and social networking sites which facilitate
infidelity. The remaining 34 domains linked to 1,324 ads are
not at all relevant to IPS.
We analyzed the 598 search terms that returned ads across
all measurement periods. We determined whether each term
explicitly indicated that the searcher intended to engage in IPS.
Terms that indicated the intent to track a cell phone but did not
indicate that it was another person’s phone (such as “best free
17
gps phone tracking app”) or that indicated the intent to track a
child’s phone (such as “free family tracker app”) were labeled
“relevant” but not explicit. Terms that discussed a spouse but
did not mention tracking (such as “cheating spouse forum”)
were also marked relevant but not explicit. Of the 598 search
terms, 135 were explicit, 324 were relevant to IPS but not
explicit, and 139 were irrelevant (e.g., “Spyro the Dragon”). Of
12,484 observed ad impressions, 58% were on explicit terms,
39% on relevant terms and 3% on irrelevant terms.
We further examined the 3,128 ad impressions shown for
the 22 domains that sold IPS-usable software. Of these, 1,203
(38%) were shown on IPS-explicit terms, 1,920 were shown
on IPS-relevant, but not explicit, terms, and four were shown
on irrelevant terms. The rate of ads on IPS-explicit terms for
specific apps ranged from 0%, in the case of TeenSafe, (the one
app that admonished us when speaking to customer service,
590 total ad impressions) to 91% in the case of RemoteCellSpy
(418 total ads). Though further study is required to find out
which words in our search term is triggering the ad, the
discrepancy in the number of IPS-explicit terms showing ads
for one company but not for another seems to indicate that
some companies are actively trying to advertise for IPS use.
18
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