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Breaching the Human Firewall: Social engineering in Phishing and Spear-Phishing Emails

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We examined the influence of three social engineering strategies on users' judgments of how safe it is to click on a link in an email. The three strategies examined were authority, scarcity and social proof, and the emails were either genuine, phishing or spear-phishing. Of the three strategies, the use of authority was the most effective strategy in convincing users that a link in an email was safe. When detecting phishing and spear-phishing emails, users performed the worst when the emails used the authority principle and performed best when social proof was present. Overall, users struggled to distinguish between genuine and spear-phishing emails. Finally, users who were less impulsive in making decisions generally were less likely to judge a link as safe in the fraudulent emails. Implications for education and training are discussed.
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Australasian Conference on Information Systems Butavicius et al.
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Breaching the Human Firewall: Social engineering in
Phishing and Spear-Phishing Emails
Marcus Butavicius
National Security and Intelligence, Surveillance and Reconnaissance (ISR) Division
Defence Science and Technology Group
Edinburgh, South Australia
Email: marcus.butavicius@dsto.defence.gov.au
Kathryn Parsons
National Security and Intelligence, Surveillance and Reconnaissance (ISR) Division
Defence Science and Technology Group
Edinburgh, South Australia
Email: kathryn.parsons@dsto.defence.gov.au
Malcolm Pattinson
Business School
University of Adelaide
Adelaide, South Australia
Email: malcolm.pattinson@adelaide.edu.au
Agata McCormac
National Security and Intelligence, Surveillance and Reconnaissance (ISR) Division
Defence Science and Technology Group
Edinburgh, South Australia
Email: agata.mccormac@dsto.defence.gov.au
Abstract
We examined the influence of three social engineering strategies on users judgments of how safe it is
to click on a link in an email. The three strategies examined were authority, scarcity and social proof,
and the emails were either genuine, phishing or spear-phishing. Of the three strategies, the use of
authority was the most effective strategy in convincing users that a link in an email was safe. When
detecting phishing and spear-phishing emails, users performed the worst when the emails used the
authority principle and performed best when social proof was present. Overall, users struggled to
distinguish between genuine and spear-phishing emails. Finally, users who were less impulsive in
making decisions generally were less likely to judge a link as safe in the fraudulent emails. Implications
for education and training are discussed.
Keywords
human-computer interaction, cyber security, phishing, empirical evaluation
1 Introduction
Phishing emails are emails sent with malicious intent that attempt to trick recipients into providing
information or access to the sender. Typically, the sender masquerades as a legitimate entity and crafts
the email to try and persuade the user to perform an action. This action may involve revealing sensitive
personal information (e.g., passwords) and / or inadvertently providing access to their computer or
network (e.g., through the installation of malware) (Aaron and Rasmussen 2010; APWG 2014; Hong
2012). In a recent survey of Australian organisations, the most common security incident reported
(45%) was that of employees opening phishing emails (Telstra Corporation 2014). While the direct
financial costs of such cyber-attacks in 2013 is estimated at a staggering USD $5.9 billion (RSA
Security 2014), there are also a range of other negative consequences to organisations that can be just
as harmful (Alavi et al. 2015). These include damage to reputation, loss of intellectual property and
sensitive information, and the corruption of critical data (Telstra Corporation 2014).
A more sinister development in cyber-attacks has been the increase in spear-phishing (Hong 2012). In
contrast with phishing emails, which tend to be more generic and are sent in bulk to a large number of
recipients, spear-phishing emails are sent to, and created specifically for, an individual or small group
of individuals (APWG 2014). When directed towards senior executives and high-ranking staff, such
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attacks are known as 'whaling'. These targets typically have greater access to sensitive corporate
information and may have privileged access accounts when compared to the average user. Spear-
phishing emails include more detailed contextual information to increase the likelihood of a recipient
falling victim to them (Hong 2012). For example, they may include information relevant to the
recipient’s personal or business interests to increase the likelihood that the recipient will respond.
Such attacks are increasingly deployed by criminals who are attempting to commit financial crimes
against specific targets, corporate spies involved in stealing intellectual property and sensitive
information, and hacktivists who wish to draw attention to their cause (APWG 2014).
Phishing and spear-phishing remain ongoing threats because they circumvent many technical
safeguards by targeting the user, rather than the system (Hong 2012). Previous phishing studies have
attempted to understand these human issues by studying the visual and structural elements of emails
that influence people (Jakobbsson 2007; Furnell 2007; Parsons et al. 2013). However, phishing emails
also frequently use social engineering to coerce the target into responding (Samani and McFarland
2015), and there is a lack of research examining the influence of social engineering strategies.
1.1 The Influence of Social Engineering Strategies
Social engineering refers to the psychological manipulation of people into disclosing information or
performing an action (Mitnick et al 2002). This paper focuses on how three different social
engineering strategies influence users’ response to emails. To our knowledge, no previous studies on
phishing have manipulated social engineering strategies in a controlled user study. However,
psychological persuasion has been studied extensively in other contexts such as advertising and
helping behaviour (Knowles and Lin 2004).
Although there is disagreement in the literature as to how to categorise persuasion strategies (Shadel
and Park 2007; Pratkanis 2007), the most widely accepted classification of psychological persuasion
strategies is by Cialdini (2007). Cialdini’s (2007) summary includes six principles of persuasion. Three
of the tactics, namely, reciprocation, consistency and liking, are more dependent on a mutual,
recurring relationship, and are therefore less suited to the lab-based scenario of our study, in which
the users do not have any relationship with the sender. Hence, our study focused on Cialdini’s (2007)
other three principles: social proof, scarcity and authority.
Social proof suggests that people are more likely to comply with a request if others have already
complied (Cialdini 2007). In a phishing context, emails that specify the offer has already been taken up
by other people are likely to be more persuasive. Scarcity is based on the idea that people are more
likely to value something that is rare or limited. Hence, people are more likely to be influenced by
emails that claim an offer is only available for a short time. The authority principle indicates that
people are more likely to comply with a request that appears to be from a respected authority figure.
Hence, an email with a request from the CEO of an organisation should be more effective than the
same request from a less influential person. A recent survey of phishing emails reported that, between
August 2013 and December 2013, authority was the most prevalent social engineering technique used
in such attacks followed closely by scarcity, particularly in emails that requested information on
account details (Akbar 2004).
1.2 The Design of Phishing Studies
There are only two previous studies on human susceptibility to phishing emails that have involved the
direct manipulation of Cialdini’s (2007) influence techniques. Neither of these were controlled user
studies, and they yielded contradictory results. While Wright et al. (2014) found that authority was the
least influential technique in tricking people into falling for phishing scams, Halevi et al. (2015) found
the same strategy to be the most influential. Both these studies used the methodology that has been
become known in the literature as 'real phishing’, whereby users unknowingly receive emails as part of
the test in their normal inbox (see also Jagatic et al. 2007).
To address these contradictory findings and further examine the issue of how Cialdini’s techniques
may influence people’s susceptibility to phishing emails, we decided to use an alternative, lab-based
approach (see also Parsons et al. 2013; Pattinson et al. 2012). Using this methodology, users were
presented with emails in a controlled setting and their behaviour was logged. While such studies may
lack the real-world face validity of 'real phishing’ experiments, they have the advantage that they
provide greater control and more comprehensive measurement of user behaviour. For example, ‘real
phishing’ studies do not measure how people make decisions on genuine emails. In our study, by
testing performance on both genuine and fraudulent emails, we can apply an approach to evaluation
known as Signal Detection Theory (SDT: Green and Swets 1966). Previously, we applied this approach
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to the analysis of human detection performance of phishing emails (Parsons et al. 2013). SDT has also
been applied to a wide range of other applications including human face recognition and image
identification, biometric system assessment, economics and neuroscience (Butavicius 2006; Fletcher
et al. 2008; Gold and Shadlen 2007; Hanton et al. 2010). SDT allows us to estimate two measures:
discrimination and bias. Discrimination measures how well people can distinguish between genuine
and fraudulent emails and bias measures people’s tendency to classify an email as either genuine or
fraudulent. In contrast, real phishing’ studies cannot estimate discrimination and bias measures
because they only collect behavioural responses to phishing emails1.
1.3 Individual differences
Finally, we need to understand what makes some individuals better at detecting phishing emails than
others. Halevi et al. (2015) and Pattinson et al. (2012) have shown that a number of individual
differences (e.g., personality characteristics and familiarity with computers) can influence how people
respond to phishing emails. In the current study, we included the Cognitive Reflection Test (CRT:
Frederick 2005), which measures how impulsive people are when making decisions (i.e., cognitive
impulsivity). Sagarin and Cialdini (2004) have argued that resisting persuasion techniques requires
more cognitive resources than accepting them. Accordingly, previous research has shown that higher
individual levels of impulsivity in decision making are associated with poorer performance in the
detection of phishing emails (Parsons et al. 2013). In this study, we sought to replicate this finding. In
addition, we tested whether cognitive impulsivity was associated with the ability to detect spear-
phishing emails. By understanding what individual differences influence information security
behaviours, we can begin to assist in the training and education of users to resist phishing attacks.
1.4 Aims of the research
In summary, the current study seeks to address the following questions:
How do the three social engineering strategies of authority, scarcity and social proof
influence users’ judgments on the safety of links in emails?
Does the influence of these techniques vary across different types of emails, i.e., genuine,
phishing and spear-phishing emails?
How well can people detect phishing and spear-phishing emails?
How does a user’s impulsivity in making decisions affect their ability to judge the safety of a
link in an email?
In what follows, we will describe the methodology of our experiment, present a statistical analysis of
the results of our study, and then discuss the findings and implications of this work, with a focus on
training and education.
2 Methodology
2.1 Participants
Our convenience sample consisted of 121 students from a large South Australian university, and they
were recruited via email invitation. At the time of the study, these students were currently enrolled in
undergraduate and postgraduate level courses including finance, international business, accounting,
marketing, management and entrepreneurship. Approximately half of the participants (60) had
undertaken most of their tertiary education in Australia. The majority of the students were female
(68%), all were 18 years or older and most were between 20-29 years of age (62%).
2.2 Emails
Our experiment used 12 emails, which were either genuine, phishing or spear-phishing emails. To
create the emails, we consulted with university IT security staff, who provided examples of phishing
emails that had been sent to university email accounts. These phishing emails had been sent within the
previous six months and, based on recipient-reporting and system monitoring, had been identified as
the most successful attacks against students and staff. These standard phishing emails (i.e., not spear-
1 ‘Real phishing’ studies can only calculate hits (i.e., the number of correct detections of a phishing
email) but not false alarms (i.e., the number of incorrect judgments of a genuine email as phishing).
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phishing) were used as templates to form the phishing emails in our experiment. For safety purposes,
we disabled students access to the internet during the study, and also modified the actual phishing
link by a single character. We also collected genuine emails that had been received by students of the
university to provide as a template for the remaining emails. These were used to create the genuine
and spear-phishing emails in our study, where the only difference between the two emails was the link.
For genuine emails we used a legitimate link, while for spear-phishing emails, we used the modified,
illegitimate links from the actual phishing emails as previously specified.
In all phishing and spear-phishing emails, the displayed text for a link was a description such as “Click
here” or “Take the surveyrather than the actual link, and participants were advised, both verbally and
in writing at the start of experiment, that if they “hover over a link, it will show you where it would take
you”. Although the names and contact details in the emails were fictitious, the position titles in the
genuine and spear-phishing emails were actual positions at the university. Participants were advised
that, when judging the emails, they were to assume that the emails had all been sent to them
deliberately (i.e., they had not received them by mistake) and that the topics in the emails were
relevant to them (i.e., “if the email mentions a piece of software, assume that you are interested in that
software”).
In order to include the appropriate social engineering strategy, we added phrases to the emails that
appealed to these strategies. There were four conditions testing the effects of social engineering:
Authority: The email appeared to come from a person or institution of authority (e.g., CEO,
CIO) and the language used was more authoritative.
Social proof: The email encouraged the participants to take a particular action because other
people, often peers, had already undertaken this action (e.g., “Over 1000 students will
study overseas in 2014. Will you be one of them?”).
Scarcity: The email includes information that suggests an offer is limited (e.g., they have a
limited time to respond or that there are a limited number of places available on a course).
None: The email did not contain any phrases appealing to authority, social proof or scarcity
strategies.
Each participant saw the same 12 emails. For each type of email (i.e., genuine, phishing and spear-
phishing), we applied each of the four social engineering treatments once (i.e., authority, social proof,
scarcity and none).
2.3 Procedure
Participants were allocated to separate lab-based sessions with a maximum of twenty students in each.
Each student completed the experiment independently via computer. A research assistant explained
the procedure and remained present in the room throughout the experiment to answer any questions
and to ensure students worked independently. Participants were not explicitly told they were
participating in an experiment on phishing. This is because previous research has shown that
informing people they will view phishing emails artificially raises their awareness of phishing attacks
for the duration of the experiment via a psychological process known as priming (Parsons et al. 2013).
The experiment was delivered using the Qualtrics online survey software. Participants were shown
each email separately and were asked to provide a ‘Link Safety’ judgment (i.e., ‘It is okay to click on the
link in this email’.). Responses were provided on a five point Likert scale where “1 = strongly disagree,
“2” = disagree, “3” = neither agree nor disagree, “4” = agree and “5” = strongly agree. The emails were
presented to participants in a different, random order for each session. After participants had judged
all emails, they were then asked to complete the CRT in Qualtrics.
3 Results
To summarise the overall results, we recoded the ‘Link Safety’ judgments into a binary variable (‘Safe
to click?’) such that scores of 4 (‘agree’) and 5 (‘strongly agree’) were classified as ‘safe’ and all
remaining responses were classified as ‘unsafe’. A summary of all participants’ responses to links
within the experiment can be seen in Figure 1. Participants correctly determined that legitimate links
in genuine emails were safe to click 77% of the time. However, in spear-phishing emails, where the link
was always unsafe, they incorrectly judged the link to be safe 71% of the time. Almost half the sample
(45%) did not judge any of the links in the spear-phishing emails as unsafe. For standard phishing
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emails, the percentage of responses that incorrectly judged the link to be safe dropped to 37%. 10% of
the participants did not judge any of the links in the phishing emails as unsafe.
Next we analysed performance using a 4 x 3 Repeated Measures Analysis of Variance on the original
five point Link Safety ratings. There were four levels of social engineering strategy: scarcity, social
proof, authority and none. There were three levels of email type: genuine, phishing and spear-
phishing. As displayed in Figure 2, there was a significant overall influence of email type (Wilks'
Lambda = .38, F(2,119) = 80.09, p < .001, multivariate = .62). In other words, there was a
significant variation in decisions on the safety of the link depending on whether the email was genuine,
phishing or spear-phishing.
There was also a significant influence of social engineering strategy on the ‘Link Safety judgments of
participants (Wilks' Lambda = .85, F(3,118) = 6.89, p < .001, multivariate = .15). Overall,
participants judged the links in phishing emails that conveyed authority as the safest (see Figure 2).
Pairwise comparisons showed that the mean ‘Link Safety’ rating when the authority tactic was present
was significantly higher than those for the other social engineering strategies (Mean Authority Scarcity =
.32, CI95% = [.12, .525], SE = .08, p < .001; Mean Authority Social Proof = .33, CI95% = [.11, .55], SE = .08, p <
.05). The mean for authority, although higher than the mean for emails with an absence of any social
engineering strategy, was not significantly so (Mean Authority None = .198, CI95% = [-.02, .42], SE = .08, p
= .097).
Figure 1: Summary of ‘Safe to click?’ judgments across the experiment. Results are displayed for the
three types of emails (genuine, spear-phishing and phishing). Correct responses are indicated in
grey, while incorrect responses are shown in black.
As can be seen in Figure 2, there was a significant interaction between the main effects of social
engineering strategy and email type (Wilks' Lambda = .471, F(6,115) = 21.5, p < .001, multivariate =
.53). While the effect of social engineering strategy was similar for genuine and spear-phishing emails,
the influence of those strategies was qualitatively different for phishing emails. Specifically, for
phishing emails, when there was an absence of any social engineering strategy, the mean ‘Link Safety’
score was actually higher than when a social engineering strategy was present. In addition, the lowest
mean rating was associated with the social proof attempts.
Using the Signal Detection Theory (SDT) approach, we calculated A’ and B’’ which are non-parametric
measures of discrimination and bias, respectively (Stanislaw & Todorov, 1999). Discrimination
measures how well someone can distinguish between a fraudulent email and a genuine email. A score
of 1 for A’ means that discrimination ability is perfect while a score of 0.5 means that fraudulent emails
cannot be distinguished from genuine emails. Bias measures someone’s tendency to respond one way
or the other, i.e., their bias towards saying an email is fraudulent or that it is genuine, regardless of
2
p
2
p
2
p
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how well they can discriminate between them. B’’ scores can range from -1 (everything is classified as
fraudulent) to 1 (everything is classified as genuine) while zero indicates no response bias.
Figure 2: Errorbar plot of means (+/- 1 SE) for ‘Link Safety’ ratings for each combination of Social
Engineering Strategy (Y axis) and Deceit Effort (separate lines).
First, we looked at these SDT measures in relation to detecting spear-phishing emails (see Table 1).
According to the SDT framework, the decision-making task of the user is to distinguish between a
‘signal’ and ‘noise’ (Swets 1966). Using the binary variable ‘Safe to click?’, we defined noise trials as
cases where the email was genuine, and signal trials as the spear-phishing emails. As described in
Section 2.2, spear-phishing emails differed from the genuine emails only in the maliciousness of the
embedded link. In this way, the ‘signals’ the user are trying to detect are the spear-phishing attempts,
and the only cue is the legitimacy of the link. Secondly, we calculated SDT measures for users’ ability to
detect phishing emails. In this way, the ‘signals’ that the user are trying to detect are the phishing
attacks and the distinguishing cues may include not just the hyperlink but also legitimacy of the
sender, consistency and personalisation and spelling or grammatical irregularities (see Parsons et al.
2015).
Authority
Scarcity
None
Spear-
phishing
A’
0.5
0.51
0.59
B’’
0
0.01
0.07
Phishing
A’
0.72
0.82
0.67
B’’
0.14
0.03
0.11
Table 1. Signal Detection Theory measures for phishing and spear-phishing emails across the
different social engineering conditions.
Not surprisingly, users were better able to detect phishing emails (Mean A’ = 0.78) than spear-
phishing emails (Mean A’ = 0.59). The relative effectiveness of the different social engineering
strategies was the same for phishing and spear-phishing emails. Authority was the most successful
strategy for confusing individuals as to the legitimacy of the fraudulent email and social proof was the
least successful. When the fraudulent email used the authority strategy, participants were unable to
reliably detect spear-phishing at all (A’ = 0.5).
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The major difference between the two analyses was for the emails with an absence of any social
engineering strategy. For these emails, the ability to discriminate between genuine and fraudulent
emails was relatively high for the spear-phishing emails (i.e., second best after social proof) whereas it
was relatively lower for standard phishing emails (i.e., performance was worst of all conditions). In
detecting phishing and spear-phishing attacks, users were biased towards responding that an email
was legitimate in all but one of the conditions of the experiment.
Averaged ‘Link Safety judgments for individuals were compared against their scores on the CRT using
Spearman’s rank correlation coefficients (ρ). There was a significant negative correlation between CRT
scores and link safety judgments for spear-phishing (ρ = -.23, p = .014, N = 112) and phishing (ρ = -.3,
p = .001, N = 112) emails. In other words, participants who were less impulsive in decision-making
were more likely to judge a link in a fraudulent email as unsafe. However there was no significant
correlation between performance on the CRT and link safety judgments on genuine emails (ρ = -.01, p
= .973, N = 114).
4 Discussion
In our study, the social engineering strategy that was most likely to influence users to judge that an
email link was safe was authority, and the least effective strategy was social proof. The effectiveness of
authority in our experiment, although in contrast with Wright et al.’s (2014) findings, supports the
results of Halevi et al. (2015). In addition, our results concur with lab-based research into social
engineering strategies in messages within emails (Guéguen and Jacob 2002) and marketing (Sagarin
and Cialdini 2004) and are consistent with extensive research in other areas of psychology that suggest
a strong tendency for people to be obedient towards authority (Blass 1999; Milgram 1974). The relative
effectiveness of the social engineering strategies in our study was similar for both phishing and spear-
phishing emails.
Overall, users demonstrated a bias towards classifying an email as genuine rather than fraudulent
which is to be expected given that most emails in the wild are in fact genuine. Given the additional
contextual information included in spear-phishing emails, it was also not surprising that participants
were far worse at detecting them than the generic phishing emails in our experiment. However, what
was alarming was the particularly poor performance of participants in trying to detect spear-phishing
emails when appeals to authority were present. Taken as a whole, the participants were unable to
reliably distinguish between spear-phishing and genuine emails when the email contained reference to
an authority figure. What makes this particularly concerning is that:
a) the heightened effort and vigilance expected of users in a lab-based experiment should
improve performance in comparison to real life,
b) participants were explicitly told how to check the real destination of a link in an email before
the start of the experiment, and
c) the malicious link destinations were obviously unrelated to the content of the email.
Our findings are particularly worrying given the increase in spear-phishing in the wild reported in
recent analyses of cyber-attacks (APWG 2014; Hong 2012; Samani and McFarland 2015) and the
dominance of the authority persuasion technique within them (Akbar 2014). In fact, the success of
such deceitful tactics, as demonstrated in our study, may partly explain their increased popularity.
Interestingly, the use of any social engineering technique in phishing emails appeared less effective
than no technique at all. This may be due to an inoculation effect against this type of persuasion
(McGuire 1970), whereby users have been exposed to so many generic phishing emails that attempt to
use social engineering, that they have learnt to resist the persuasion attempt and not to respond to
them. Such inoculation to persuasion has been demonstrated in marketing contexts (Friedstat and
Wright 1994; Szybillo and Heslin 1973). However, a simpler explanation may also account for the
findings. It may be that the presence of any social engineering strategy in standard phishing emails,
where no significant effort has been made to target an individual using inside knowledge, is in fact a
cue to the malicious intent behind the email. Without the necessary context, the persuasion may
appear inappropriate and therefore raise the suspicions of the user.
Participants who were less impulsive in decision making were more likely to judge the links in
phishing emails as more dangerous. Our findings replicated those of previous research that found that
lower cognitive impulsivity was associated with resistance to phishing email attacks (Parsons et al.
2013). However, our results have also found that lower cognitive impulsivity can protect against
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targeted, high effort attacks such as spear-phishing. In addition, lower cognitive impulsivity did not
adversely influence the judgments of genuine emails.
One of the limitations of our study was the use of a convenience sample of university students enrolled
in subjects on business and information systems. Such a sample may not necessarily reflect the
abilities of the wider population and, therefore, this limits the generalisability of our findings. As a
result, we propose that future research should seek to replicate our study on a larger, more diverse
sample.
The fact that our study found a potential link between someone’s preference for a decision making
style and their susceptibility to phishing has implications for future research in this area and,
ultimately, the development of a training solution. Cognitive impulsivity is linked to what is known as
dual processing models of persuasion (Chaiken et al. 1996). These models assume that we have two
modes of processing information. The first mode, known as the ‘central’ mode, uses systematic
processing that is highly analytical and detailed. The second mode, known as the ‘peripheral’ mode, is
heuristic in nature and is more influenced by superficial cues. By using heuristics rather than detailed
analysis, the ‘peripheral mode’ is faster and uses fewer cognitive resources than the ‘central’ mode.
Humans have evolved to use a large number of heuristics that allow us to function effectively in a
range of different scenarios (Gigerenzer et al. 1999). However, this efficiency comes at a cost because
these heuristics are less-accurate than the analytical approach associated with the ‘central’ mode. The
CRT measures someone’s tendency to use the ‘central’ mode more than the ‘peripheral’ mode and
therefore can account for the increase in errors in judging emails by people high in cognitive
impulsivity.
Research has shown that our style of decision making can be modified, at least in the short term. For
example, Pinillos et al. (2011) showed that completing the CRT itself can activate ‘central’ mode
processing for subsequent tasks. Therefore, training people to defend against phishing attacks could
focus on activating ‘central’ mode processing when people are judging emails. In the short-term, future
research should investigate whether pre-testing with the CRT can improve phishing email
discrimination. In the long-term, research may involve the development of structured analytic
techniques similar in style to the techniques that are commonly used by intelligence analysts (e.g.,
Heuer 1999). Such techniques activate the ‘central’ mode of processing so that an analyst is less likely
to make an incorrect assessment of intelligence by falling back on our natural tendency towards faster,
but less accurate ‘peripheral’ processing. A possible training solution to phishing may require that we
develop and teach analogous structured analytic techniques for assessing the legitimacy of emails. In
other words, rather than simply warning users about the threat posed by malicious emails or providing
them with specific examples, we may eventually be able to train people to use more effective strategies
to detect phishing and spear-phishing attacks.
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Acknowledgements
This project was supported by a Premier’s Research and Industry Fund granted by the South
Australian Government Department of State Development.
Copyright
Copyright: © 2015 authors. This is an open-access article distributed under the terms of the Creative
Commons Attribution-Non Commercial 3.0 Australia License, which permits non-commercial use,
distribution, and reproduction in any medium, provided the original author and ACIS are credited.
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