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Introductory Chapter: Computer Security Threats

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Introductory Chapter: Computer
Security Threats
1. Introduction
Along with the tremendous progress in Internet technology in the last few
decades, the sophistication of the exploits and thereby the threats to computer sys-
tems have also equally increased. The exploitation is done by malicious hackers who
find vulnerabilities or weaknesses, which are the pre-existing errors in the security
settings in the computer systems. The common types of vulnerabilities are errors in
the design or configuration of network infrastructure, protocols, communication
media, operating systems, web-based applications and services, databases, etc.
Threat is a potential risk that exploits a vulnerability to infringe security and
cause probable damage/disruption to the information/service stored/offered in/by
computer systems or through communication links. A threat to a computer systems
occurs when the confidentiality (preventing exposure to unauthorized parties),
integrity (not modified without authorization), and availability (readily available
on demand by authorized parties) of information on systems are affected. Thus,
a computer system threat in general can include anything deliberate, unintended,
or caused by natural calamity that effects in data loss/manipulation or physical
destruction of hardware. Accordingly, the threats on computer system are classified
as physical threats and nonphysical threats. Physical threats cause impairment to
hardware or theft to system or hard disk that holds critical data. Nonphysical threats
target the data and the software on the computer systems by corrupting the data or
by exploiting the errors in the software.
The exploits when successful result in security attacks on computer systems.
Hence, threat is a possible danger caused by system vulnerability, while attack is the
attempt of unauthorized action or a harmful action. The realization of a threat is
usually detrimental and is termed an attack.
In this introductory chapter, the computer security threats are defined as prob-
able attacks from hackers that let them to gain illicit entree to a computer. In this
chapter, a detailed introduction is given on the common computer system threats.
The logical threats are a main cause of security incidents on computer systems.
Knowing these threats and their characteristics helps in identifying the threats
and to proactively devise steps in protecting the systems. The organization of
this chapter is as follows. Section 2 introduces the motivation and objective of the
hackers. Section 3 is on the classification of threats, which also includes an exhaus-
tive coverage of all the threats. The details of the top security menaces of 2020 and
the expectation for the latter half of 2020 are introduced in Section 4. Section 5
concludes the chapter.
Computer Security Threats
2. Motivation and objectives of hackers
The purpose of a hacker is to break the security of computers and networks
affecting the confidentiality, integrity, and availability of information/service on
systems. Such activities of hackers are considered illegal as they invest their time
and know how, to make personal gains and breach the security across networks.
Before looking at the taxonomy of computer threats, it is necessary to classify
the different types of hackers. Each type of hacker is expected to have their own
motivation for their activities. The most common of those are included here:
Fun: Fun is the only motivation for the script kiddies and lot of nonserious hack-
ers. For them, the breaking into a secure system is a challenging and adventurous
enjoyable game to test their wits and skills.
Vulnerability testing: Vulnerability testing is done by administrators to locate
vulnerabilities and hence develop protections. The same is also done by hackers to
identify vulnerabilities in target systems and to find the exploits for those vulner-
abilities. This is almost a pre-phase of an attack.
Theft: Theft or stealing of data is when hackers infiltrate on a database of
credentials of individuals or organizations.
Espionage: Espionage is another type of theft where the hacker tries to get pro-
tected information instead of the direct financial gain. The information stolen can
be either sold in black market or used by adversaries to gain strategic advantages.
Spamming: Spamming is not just about unsolicited emails. This spam can be
due to certain particular malware that invade the web browser and devastate with
unwanted ads.
Control: The hacker uses a Trojan or other means to take remote control over
another system. Then the hacker can turn that compromised system into a bot or
a zombie computer that they use to power spam or to deploy distributed denial of
service attacks.
Disruption: Disruption of services or access to information, by taking over web-
sites or social media accounts, is usually an act of competition, protest, or rivalry.
This effect will slow down or shut down of the target’s Internet activity.
3. Classification of computer threats and attacks
Computer threats and attacks involve accessing information, obliterating or
manipulating data, destabilizing the computer, or degrading its performance [1].
Computer attacks are mainly information gathering, privilege escalation, buffer
overflow exploits, remote accessing by unauthorized users, and denial of service
attacks [2]. Network attacks being a subset of computer attacks were mostly
attacks on computer systems that form the basic infrastructure of a communica-
tion network. A network aids in sending an attack or it could be the means of
There are various steps involved in the attacking scenario, and these steps are
briefly listed here:
Step 1: spoofing
Before initiating any of the attacking steps, the hackers normally prefer to hide
their identity and their activities. These are normally done by spoofing when the
attacker hides his identity and pretends to be someone else. This can be done by
MAC cloning, IP spoofing, or email spoofing.
Step 2: reconnaissance
It is always a good practice to plan well before undertaking any action, and this
is applicable in the case of hacking too. The hackers first identifies a target to launch
Introductory Chapter: Computer Security Threats
an attack, extract maximum information regarding this target, understand its
vulnerabilities, and then only explore the best ways to exploit it.
Step 3: weaponization
The hacker with the information collected in the previous phase identifies/
develops weapons in order to get into the computer or the network. During this
phase, the hacker collects the tools that they plan to use once they gain access to the
system for the successful exploitation of the vulnerabilities in the system.
Step 4: implementation
In the implementation phase, the attack starts working. It is when the phish-
ing e-mails are sent or when the fake web pages are posted to the Internet and the
attacker patiently waits for all the data they need to start rolling in.
Step 5: exploitation
This is a state when the sensitive and confidential data starts rolling in. It is the
most exciting phase for the hackers, and they try out the usernames and passwords
against web-based e-mail systems or secured connections to sensitive networks.
Step 6: installation
After a successful exploitation, the attacker will make sure to have continued
access to the system. This is by installing a persistent backdoor or creating admin
accounts on the system, disabling firewall rules, and perhaps even activating remote
desktop access on computer systems on the network.
Step 7: control
Once the attacker gains access to the network or creates administrator accounts
or installs all the necessary tools for backdoor entry any time to the system, the
attacker is in control of the target.
Step 8: action on set goals
With total control on the target system, the attacker can set goals and achieve it
with or without the knowledge of the genuine user.
The attacks are thus classified depending on the various steps taken by the
hacker in the process of the attack, starting from hiding the identity to information
collection, which is the pre-phase of an attack, to the actual attack.
4. Computer threats
4.1 Spoofing
Spoofing is when someone hides their identity to evade detection for their wrong
acts and pretends to be someone else in an attempt to gain trust and get sensitive
system information. The common spoofing done by changing the hardware or MAC
address is called MAC cloning, changing the IP address or the unique identity on
the network is called IP spoofing, and impersonating as someone else in their digital
communication is called email spoofing.
4.2 Information-gathering attacks
Information gathering is the practice of attacker gaining priceless details about
probable targets. This is not an attack but only a pre-phase of an attack and is totally
passive as there is no explicit attack. Systems including computers, servers, and net-
work infrastructure, including communication links and inter networking devices,
are sniffed, scanned, and probed for information like whether the target system is
up and running, what all ports are open, details regarding the operating system and
its version, etc. Some of the information-gathering attacks are sniffing, mapping,
vulnerability scanning, phishing, etc.
Computer Security Threats
4.3 Password attacks
The simplest way to achieve control of a system, or any user account, is through
a password attack. If the personal and behavioral details of the victim are known,
the attacker starts with guessing password. Frequently, the attacker uses some form
of social engineering to trace and find the password. Dictionary attack is the next
step in password attacks and is automated.
4.4 Malware
After gaining access to a system, the attacker takes the support of malware or
malicious software that clandestinely acts against the interests of the computer user.
4.5 Virus
Computer viruses are the most communal threat to the computer users.
Computer viruses are malicious software designed to blow out from one computer
to another through file transfer, piggybacks on genuine programs and OS, or
e-mails. The email attachments or downloads from particular websites contaminate
the computer and also other computers on its list of contacts by using the commu-
nication network. Viruses influence the system security by changing the settings,
accessing confidential data, displaying unwanted advertisements, sending spam to
contacts, and taking control of the web browser [2]. The viruses are identified as
executable viruses, boot sector viruses, or e-mail viruses.
4.6 Worms
Computer worms are fragments of malicious software that reproduce swiftly
and blow out from one computer to another through its contacts, again spreading to
the contacts of these other computers and so on and reaching out to a large number
of systems in no time. Captivatingly, worms are prepared for spreading by exploit-
ing software vulnerabilities. Worms display unwanted advertisements. It uses up
tremendous CPU time and network bandwidth in this process thereby denying
access to the systems or network of the victim, creating chaos and trust issues on a
communication network.
4.7 Trojans
Trojans are programs that appear as perfectly genuine but, in reality, have a
malicious part embedded in it. Trojans are spread usually through email attach-
ment from the trustworthy contacts and also on clicking on fake advertisements.
The payload of Trojans is an executable file that will install a server program on
the victims system by opening a port and always listening to that port whereas the
server is run on the attacker’s system. Hence, whenever the attacker wants to login
to the victim machine, they can do so by means of the backdoor entry making it
hidden from the user.
4.8 Spyware and adware
Spyware and adware are software with a common property of collecting
personal information of users without their knowledge. Adware is intended
to track data of the user’s surfing behaviors, and, based on that, pop-ups and
advertisements are displayed. The adware clause in the agreement during the
Introductory Chapter: Computer Security Threats
installation process is often skipped with least seriousness. Spyware on the other
hand gets installed on a computer and gathers information about the user’s online
activities without their knowledge. Spyware contains keyloggers that record every-
thing typed on the keyboard, making it unsafe due to the high threat of identity
4.9 Scareware
Scareware is yet another malware that tricks victims by displaying fake alerts
and forcing the victim to buy protective software that is fraudulent. The alerts or
the pop-up messages sound like warning messages along with proper protective
measures, which if followed creates security issues.
4.10 Rootkit
Rootkit is a pool of software tools that gets mounted in stealth along with some
genuine software. Rootkit allows remote access and administrative control on a sys-
tem. With these privileges, the rootkit performs malicious activities like disabling of
antivirus, password sniffing, keylogging, etc.
4.11 Keylogger
Keylogger software has the ability to record keystrokes and also capture screen-
shots and save it to a log file in encrypted form. Keylogger software can record all
the information that is typed on the keyboard including passwords, e-mail, and
instant messages. The log file created by the keylogger is saved and mailed to the
attacker on a remote machine with the motive to extract password and banking
details for financial fraud.
4.12 Ransomware
Ransomware is a malicious software that hampers admission to computer or files
on the computer. The computers may be locked or files encrypted. Accordingly, the
two common types of ransomware are lock screen ransomware and encryption ran-
somware. The victim will be demanded ransom for the restriction to be removed,
and this gets displayed on victim’s system. There can also be notification stating that
establishments have detected illicit activity on this computer and demands ransom
as fine to avoid prosecution.
4.13 Rogue security software
Rogue security software is another malicious program that deceives users to
believe that there is malware installed on their system or the security measures are
outdated and hence of concern. They offer installing or updating users’ security
settings. Then it is an actual malware that gets installed on the computer.
4.14 Botnets
A collection of compromised systems or bots acts as a team of infected comput-
ers under the control of a bot master to remotely control and send synchronized
attacks on a victim host. This army of bots, agents, and bot master constitute a
botnet. Botnets are used for sending spams and also for distributed denial of service
Computer Security Threats
4.15 Denial-of-service attacks
Denial-of-service (DoS) attacks as the name suggests deny users from accessing
or using the service or system. This is mainly done by overwhelming the band-
width, CPU, or memory wherein the access to the network of the victim machine or
server offering the service gets denied. DoS attacks thus interrupt the service of a
computer or network systems, making it inaccessible or too inferior in performance.
4.16 Distributed DoS
In distributed DoS (DDoS) attacks, the victim is targeted from a large number
of individual compromised systems simultaneously. The DDoS attacks are normally
done with the help of botnets. The botmaster is the attacker who indirectly attacks
the victim machine using the army of bots or zombies. The DDoS attacks occur
when a large number of compromised systems act synchronously and are being
coordinated under the control of an attacker in order to totally exhaust its resources
and force it to deny service to its genuine users. It is the upsurge in the traffic
volume that loads the website or server causing it to appear sluggish [2].
4.17 IoT-based attacks
The last decade has seen exponential increase in the use of Internet of Things
(IoT) that are smart devices used at home, organizations, and businesses. The issue
with these IoT is its weak security as these devices are often overlooked when it
comes to applying security patches that create lead-ins for attackers to seize these
devices to infiltrate the networks. An IoT-based attack is any cyberattack that lever-
ages a victims use of IoT to sneak malware onto a network.
4.18 Session hijacking
In session hijacking, the hacker takes control of a session going on between
two hosts. Session hijacking usually takes place in applications that use TCP with a
sequence number prediction. With that sequence number, the attacker sends a TCP
4.19 Blended attacks
A blended attack is a software exploit that encompasses a mixture of exploit
techniques to attack and propagate threats, for example, viruses, worms, and Trojan
4.20 Website attacks
Website attacks are targeting browser components that are at risk of being
unpatched even when the browser is patched. SQL injection attacks are intended
to target any website or web application that uses an SQL database such as MySQL,
Oracle, etc. by taking advantage of the security flaws in the applications software.
This attack is used to obtain and corrupt user’s sensitive data.
4.21 Mobile phone and VOIP threats
Malware target mobile phones, VoIP systems, and the IP PBXs as these devices
have plentiful published vulnerabilities. There are attack tools freely available on
Introductory Chapter: Computer Security Threats
the Internet, and misusing these vulnerabilities makes these attacks too common
and simple even for a script kiddie.
4.22 Wi-Fi eavesdropping
Wi-Fi eavesdropping is an attack used by network attackers to grab sensitive
information of a target system. It is the act of silently listening on an unencrypted
Wi-Fi network.
4.23 WPA2 handshake vulnerabilities
The key reinstallation attack (KRACK) lets an attacker to decipher the network
traffic on Wi-Fi routers. Every device connected to Wi-Fi, such as computers,
smartphones, smart devices, and wearables, can be identified by the hacker.
4.24 Insider attacks
One of the prevalent all-time computer security threats faced by any organiza-
tion is from its own employees. Insider attacks are initiated by disgruntled employ-
ees of an organization. Insider usually has certain privileges to the data as well as
rights on the systems and networks that they attack, giving them an advantage over
external attackers. These attacks can be hard to prevent with firewalls, which are
the first level of defense.
4.25 Supply chain attacks
A supply chain attack seeks to cause harm by targeting the least secured ele-
ments in the supply network.
4.26 Buffer overflows
Buffer overflows are used to exploit programming glitches that do not take care
of the buffer size. If a buffer is jam-packed beyond its size, the data overflows into
the contiguous memory. This flaw gets smartly used by hackers to change the execu-
tion of the program.
4.27 User to root attack
User to root attack is a case of privilege escalation where a user gains a higher
privilege than that authorized. This is not a class of attack as such, and it is the pro-
cess of any attack. Every attack will do activities the attacker is not privileged to do.
4.28 Man-in-the-middle attacks
Man-in-the-middle attacks allow the hacker to snoop on the communication
between two systems, affecting the privacy. A common method of doing this is to
place the attacker at a point and redirect all the communication through the route
that includes that hacker so that eavesdropping is possible by the hacker.
4.29 Pharming
Pharming is a widespread online fraud that will automatically point to a nasty
and illicit website by relaying the authentic URL. Even when the URL is correctly
Computer Security Threats
entered, the redirection happens to some forged website looking similar to the
actual one. This fake site prompts one to enter personal information that gets to
someone with a wicked intent.
4.30 Spam
Spams are unsolicited bulk e-mail messages that annoy the user with unwanted
and junk mails. It gives burden for communications service providers, organizations
and individuals alike. These emails can be commercial ones like an advertisement
or noncommercial one like chain letters or anecdotes. Spam is considered an active
vehicle for virus propagation, scams, fraud and is a threat to computer privacy.
Spam also phishes for interesting information with offers and promotions that trick
victims into following links or entering details.
5. Present-day computer security threats and trends
Predicting the computer security threats and trends is usually done to lend
a hand to the security experts who take proactive measures to protect security.
Normally the predictions for any year depends on how it went in the previous years,
and the changes expected are mainly in terms of the tactics and scale of the biggest
and significant threats that were successful in implementation and also in evading
detection. The investment on security is justified in many organizations only after
analyzing these predictions.
Phishing and other social engineering tactics are likely to continue in the coming
years too with increased complexity and sophistication. They will appear to be more
and more convincing to trick people into clicking on a link or opening attachments.
Even with strong defenses to protect against ransomware, hackers are expected to
all the time target more victims with large digital assets. The rise of cryptocurrency
like bitcoin will also trigger more ransomware attacks by letting demands for pay-
ment made incognito. Cryptojacking can also be seen as a common trend of future
as it involves hackers hijacking with a purpose of mining for cryptocurrency.
As the Internet of Things is becoming widely popular and more ubiquitous, the
IoT attacks will be on the upsurge. IoT includes laptops, tablets, smart wearable
devices, webcams, household appliances, Wi-Fi-enabled speakers, appliances,
alarm clocks, medical devices, manufacturing equipment, automobiles and net-
working devices like routers, gateways, switches, NAS servers, and even home
security systems. Security is rarely the first concern in the competition to bring new
products and technologies. Thus the more IoT devices, the greater the risk, making
IoT attacks to be on the rise in coming years.
Data breaches will continue in the coming years as data remains a valuable black
market attraction.
Totally new approaches for data and infrastructure protection are essential as
more and more data is moved to the cloud. Also, in the coming years, there will be
more attacks targeting electrical grids, automated transportation systems, comput-
erized water treatment facilities, etc.
State-sponsored attacks are when states or nations are using their cyber skills to
infiltrate other governments and execute attacks on severe infrastructure. As politi-
cal strains grow, state-sponsored attacks steal political and industrial secrets, spread
misinformation, perform DDoS attacks, execute prominent data breaches, etc.
Another target of attacker is the all-time sensitive medical record of patients. As
the healthcare industry gets used to the digital age, concerns around privacy, safety,
and computer security threats are also seen to rise. There are worries about a hacker
Introductory Chapter: Computer Security Threats
Author details
Directorate of Technical Education, Government of Kerala, India
*Address all correspondence to:
taking over and changing dosages of medicines, disabling vital sign monitoring,
etc., as these are life-threatening to the patients.
Now, with the self-driving cars, semiautonomous vehicles, and the connected
cars, the risk of cyber security is stringent and serious. With high-tech automobiles,
the future will likely see an increase in not only the number of connected cars but in
the number and severity of system vulnerabilities detected. For hackers, this means
yet another opportunity to exploit vulnerabilities and cause threat to life.
Endpoint security will be a major concern for organizations as malware infec-
tions of employee-owned devices are going to be a major security issue in 2020
when employees start “working from home” in the wake of COVID 19 pandemic.
When organizations permit employees not to risk their health and safety and allow
them to use their own devices, attackers will target those devices to bypass the mul-
tilayered defenses of the organization. The advantage to hackers is that the users’
personal devices are less protected compared to corporate devices as users rarely
apply added measures to protect their smart devices from impending threats.
Artificial intelligence also gets applied on both sides of the barricade for protect-
ing and attacking the computers. Artificial intelligence is being used for person
identification, threat detection, etc. to aid security; however it is also being weap-
onized by hackers to develop increasingly complex malware and attack methods.
6. Conclusion
A lot of computer threats have been included in this chapter with many terms
tending not to be mutually exclusive. Again, an attack may get classified into dif-
ferent classes since attackers use multiple techniques or strategies. The irony is that
even with lot of advanced defensive mechanism put in place by security experts,
the hackers may still use the same attacking techniques and will take advantage of
the same vulnerabilities they have used in the past. It is important to defend the
attacks by paying attention to the internal systems, deploying multiple defenses for
enhanced security, and avoiding irreparable damage. This requires the implementa-
tion of security policy as an ongoing process with tight access control mechanism
and deployment of advanced multiple layer security devices.
© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms
of the Creative Commons Attribution License (
by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,
provided the original work is properly cited.
Computer Security Threats
[1] Thomas C, Balakrishnan N.
Improvement in intrusion detection
with advances in sensor fusion. IEEE
Transactions on Information Forensics
and Security. 2009;4(3):542-551
[2] Thomas C. Performance
enhancement of intrusion detection
systems using advances in sensor fusion
[Ph. D dissertation report]; 2009
ResearchGate has not been able to resolve any citations for this publication.
Conference Paper
Full-text available
Various intrusion detection systems reported in literature have shown distinct preferences for detecting a certain class of attacks with improved accuracy, while performing moderately on the other classes. With the advances in sensor fusion, it has become possible to obtain a more reliable and accurate decision for a wider class of attacks, by combining the decisions of multiple intrusion detection systems. In this paper, an architecture using data-dependent decision fusion is proposed. The method gathers an in-depth understanding about the input traffic and also the behavior of the individual intrusion detection systems by means of a neural network supervised learner unit. This information is used to fine-tune the fusion unit, since the fusion depends on the input feature vector. For illustrative purposes, three intrusion detection systems namely PHAD, ALAD, and Snort have been considered using the DARPA 1999 dataset in order to validate the proposed architecture. The overall performance of the proposed sensor fusion system shows considerable improvement with respect to the performance of individual intrusion detection systems.
Full-text available
Various intrusion detection systems (IDSs) reported in the literature have shown distinct preferences for detecting a certain class of attack with improved accuracy, while performing moderately on the other classes. In view of the enormous computing power available in the present-day processors, deploying multiple IDSs in the same network to obtain best-of-breed solutions has been attempted earlier. The paper presented here addresses the problem of optimizing the performance of IDSs using sensor fusion with multiple sensors. The trade-off between the detection rate and false alarms with multiple sensors is highlighted. It is illustrated that the performance of the detector is better when the fusion threshold is determined according to the Chebyshev inequality. In the proposed data-dependent decision ( DD) fusion method, the performance optimization of ndividual IDSs is first addressed. A neural network supervised learner has been designed to determine the weights of individual IDSs depending on their reliability in detecting a certain attack. The final stage of this DD fusion architecture is a sensor fusion unit which does the weighted aggregation in order to make an appropriate decision. This paper theoretically models the fusion of IDSs for the purpose of demonstrating the improvement in performance, supplemented with the empirical evaluation.