Malicious Software
By
Kavita Khanna
(kavita_jairath@yahoo.com)
&
Himani Singh
(himanisingh@comcast.net)
(CS-265, Fall-2003)
Malicious Software – “Presentation Outline”
• What is malicious software?
• Categories of malicious software.
• Different malicious software – viruses,
worms, Trojan Horse etc.
• More description about viruses :
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Desirable properties of viruses.
Identifying infected files and programs.
Where do viruses reside.
Identifying and detecting viruses – virus signature.
Effect of Virus attack on computer system.
• Protection against attacks by malicious
software – preventing infection.
• References.
What is Malicious Software:

Software deliberately designed to harm
computer systems.

Malicious software program causes undesired
actions in information systems.

1.
2.
3.
4.
Spreads from one system to another through:
E-mail (through attachments)
Infected floppy disks
Downloading / Exchanging of corrupted files
Embedded into computer games
Malicious Software - Categories
Malicious Software
Viruses
Boot Viruses
Rabbit
File Viruses
Hoaxes
Time Bomb
Trojan Horse
Spyware
Logic Bomb
Trapdoor
Worms
Types of Malicious Software
• Virus : These are the programs that spread to other
software in the system .i.e., program that incorporates
copies of itself into other programs.
Two major categories of viruses:
1.
Boot sector virus :
2.
File virus :
infect boot sector of systems.
become resident.
activate while booting machine
infects program files.
activates when program is run.
Categories of Viruses
Polymorphic
Virus
Stealth
Virus
Armored
Virus
 Produces
modified & fully
operational code.
 Produces new
& different code
every time when
virus is copied &
transmitted to a
new host.
 Difficult to
detect & remove.
 Programming
tricks make the
tracing and
understanding
the code difficult.
 Complex
programming
methods used to
design code, so
difficult to repair
infected file.
 Hides
modifications it
has made to
files or to the
disk.
 Reports
false values to
programs as
they read files
or data from
storage media.
Companion
Virus
 Creates new
program instead
of modifying
existing program.
 Contains all
virus code.
 Executed by
shell, instead of
original program.
• Rabbit : This malicious software replicates itself
without limits. Depletes some or all the system’s
resources.

Re-attacks the infected systems – difficult recovery.

Exhausts all the system’s resources such as CPU
time, memory, disk space.

Depletion of resources thus denying user access to
those resources.
• Hoaxes : False alerts of spreading viruses.
 e.g., sending chain letters.
 message seems to be important to recipient, forwards
it to other users – becomes a chain.
 Exchanging large number of messages (in chain)
floods the network resources – bandwidth wastage.
 Blocks the systems on network – access denied due to
heavy network traffic.
• Trojan Horse : This is a malicious program
with unexpected additional functionality. It includes
harmful features of which the user is not aware.
 Perform a different function than what these are
advertised to do (some malicious action e.g., steal the
passwords).
 Neither self-replicating nor self-propagating.
 User assistance required for infection.
 Infects when user installs and executes infected
programs.
 Some types of trojan horses include Remote Access
Trojans (RAT), KeyLoggers, Password-Stealers (PSW),
and logic bombs.

1.
2.
3.
4.
Transmitting medium :
spam or e-mail
a downloaded file
a disk from a trusted source
a legitimate program with the Trojan inside.

Trojan looks for your personal information and
sends it to the Trojan writer (hacker). It can also
allow the hacker to take full control of your system.

1.
Different types of Trojan Horses :
Remote access Trojan takes full control of your
system and passes it to the hacker.
The data-sending Trojan sends data back to the
hacker by means of e-mail.
e.g., Key-loggers – log and transmit each keystroke.
2.
3.
4.
5.
6.
The destructive Trojan has only one purpose: to
destroy and delete files. Unlikely to be detected by
anti-virus software.
The denial-of-service (DOS) attack Trojans combines
computing power of all computers/systems it infects
to launch an attack on another computer system.
Floods the system with traffic, hence it crashes.
The proxy Trojans allows a hacker to turn user’s
computer into HIS (Host Integration Server) server
– to make purchases with stolen credit cards and
run other organized criminal enterprises in
particular user’s name.
The FTP Trojan opens port 21 (the port for FTP
transfer) and lets the attacker connect to your
computer using File Transfer Protocol (FTP).
7.
The security software disabler Trojan is designed to
stop or kill security programs such as anti-virus
software, firewalls, etc., without you knowing it.
• Spyware :
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
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Spyware programs explore the files in an
information system.
Information forwarded to an address specified in
Spyware.
Spyware can also be used for investigation of
software users or preparation of an attack.
• Trapdoor : Secret undocumented entry point to
the program.
 An example of such feature is so called back door,
which enables intrusion to the target by passing user
authentication methods.
 A hole in the security of a system deliberately left in
place by designers or maintainers.
 Trapdoor allows unauthorized access to the system.
 Only purpose of a trap door is to "bypass" internal
controls. It is up to the attacker to determine how this
circumvention of control can be utilized for his benefit.
Types of Trapdoor
Undetectable
Trapdoor
Hardware
Trapdoor
Virtually undetectable.
Security-related
hardware flaws.
•
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1.
2.
3.
4.
Worms :
program that spreads copies of itself through a
network.
Does irrecoverable damage to the computer system.
Stand-alone program, spreads only through network.
Also performs various malicious activities other than
spreading itself to different systems e.g., deleting files.
Attacks of Worms:
Deleting files and other malicious actions on systems.
Communicate information back to attacker e.g.,
passwords, other proprietary information.
Disrupt normal operation of system, thus denial of
service attack (DoS) – due to re-infecting infected
system.
Worms may carry viruses with them.
Means of spreading Infection by Worms :
• Infects one system, gain access to trusted host lists on
infected system and spread to other hosts.
• Another method of infection is penetrating a system
by guessing passwords.
• By exploiting widely known security holes, in case,
password guessing and trusted host accessing fails.
e.g., A well-known example of a worm is the ILOVEYOU
worm, which invaded millions of computers through
e-mail in 2000.
VIRUSES – More Description
Desirable properties of Viruses :
 Virus program should be hard to detect by
anti-virus software.
 Viruses should be hard to destroy or deactivate.
 Spread infection widely.
 Should be easy to create.
 Be able to re-infect.
 Should be machine / platform independent, so that it
can spread on different hosts.
Detecting virus infected files/programs :
 Virus infected file changes – gets bigger.
 Modification detection by checksum :
> Use cryptographic checksum/hash function
e.g., SHA, MD5.
> Add all 32-bit segments of a file and store the sum
(i.e., checksum).
Identifying Viruses :
 A virus is a unique program.
 It as a unique object code.
 It inserts in a deterministic manner.
 The pattern of object code and where it is inserted
provides a signature to the virus program.
 This virus signature can be used by virus scanners to
identify and detect a particular virus.
 Some viruses try to hide or alter their signature:
• Random patterns in meaningless places.
• Self modifying code – metamorphic, polymorphic viruses.
• Encrypt the code, change the key frequently.
Places where viruses live :
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Boot sector
Memory resident
Disk – Applications and data stored on disk.
Libraries – stored procedures and classes.
Compiler
Debugger
Virus checking program infected by virus – unable to
detect that particular virus signature.
Effect of Virus attack on computer system
 Virus may affect user’s data in memory – overwriting.
 Virus may affect user’s program – overwriting.
 Virus may also overwrite system’s data or programs –
corrupting it – disrupts normal operation of system.
 “Smashing the Stack” – Buffer overflow due to
execution of program directed to virus code.
Preventing infection by malicious software :
Use only trusted software, not pirated software.
Test all new software on isolated computer system.
Regularly take backup of the programs.
Use anti-virus software to detect and remove viruses.
Update virus database frequently to get new virus
signatures.
 Install firewall software, which hampers or prevents the
functionality of worms and Trojan horses.
 Make sure that the e-mail attachments are secure.
 Do not keep a floppy disk in the drive when starting a
program, unless sure that it does not include malicious
software, else virus will be copied in the boot sector.
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References:
• Webopedia.com. Trojan Horse. Retrieved Nov 8, 2003 from website:
http://www.webopedia.com/TERM/T/Trojan_horse.html
• Staffordshire University, Information & Security Team (Jun 8,
2002). Information Systems Security Guidelines. Retrieved
Nov 10, 2003 from website:
http://www.staffs.ac.uk/services/information_technology/regs/security7.shtm
• M.E.Kabay, Norwich University, VT (2002). Malicious Software. Retrieved
Nov 9, 2003 from website:
http://www2.norwich.edu/mkabay/cyberwatch/09malware.htm
• Computer Emergency Response Team (CERT), Information Security (Jul 2,
2002). Malicious Software – general. Retrieved Nov 10, 2003 from
website: http://www.ficora.fi/englanti/tietoturva/haittaohj.htm
References Cont...
• Rutgers, New Jersey (Oct 10, 2003). Trojan Horses. Retrieved Nov 10,
2003 from website: http://netsecurity.rutgers.edu/trojan.htm
• Dr. Roger R. Schell, Monterey CA (Apr 24, 2000). Malicious Software.
Retrieved Nov 11, 2003 from website: www.sp.nps.navy.mil
• Edward F. Gehringer. Computer Abuse – Worms, Trojan Horses,
Viruses. Retrieved Nov 12, 2003 from website:
http://legacy.eos.ncsu.edu/eos/info/computer_ethics/abuse/wvt/study.html
• Bullguard.com Computer Viruses. Retrieved Nov12, 2003 from website:
http://www.bullguard.com/antivirus/vi_info.aspx
• Google.com. Program Security. Retrieved Nov 12, 2003 from website:
http://www.sm.luth.se/csee/courses/smd/102/lek6-6.pdf.