2.  programs which can destroy
or cause damage to data
stored on a computer
system and to the computer
itself!
 Virus program must be
executed in order to dirty a
computer system. Viruses
can attach themselves to
other programs in order to
ensure that this happens.

3.  A computer virus is a computer program that can
copy itself and dirty a computer without
permission or knowledge of the user.

4.  Do not damage the original program or damage
the hardware
◦ May damage data files
◦ “trash” firmware
 But, some do
 For this reason most can be cleaned up with anti-
virus software.

5.  User call for a legal program
 The virus code, having inserted itself in the order
of execution, executes in its place or in addition to
the legal program.
 The virus code terminates and returns control to
the valid program

6.  Turn off file sharing on the desktop or if you
need some kind of file sharing, apply user-level
security.
 Don't open email attachments from unknown
senders, especially files with an "exe", "vbs",
"com" or "pif“.
 All downloaded files from email should be
saved to disk first and then virus scanned to
determine if they are virus free before
executing them.

7.  Displaying unwanted
messages
 Loss of Data from a
storage medium
 Computers restarting
unexpectedly
 Unwanted generation of
emails

8.  Corrupt or delete data
 Disable the computer by
changing the operating
system
 Cause silly messages to
be displayed or sounds to
be produced

9.  Worms operate
differently to viruses
 Worms can spread
themselves to other
computers without
needing to be transferred
as part of a host
program.
 The first time a user may
notice the presence of a
worm is when the
computers memory
UNEXPECTEDLY fills up

10.  A worm is self-replicating software designed to spread
through the network
◦ Can cause huge damage
 Access sensitive information
 Cause confusion by corrupting the sensitive information
 Worm vs Virus
A virus is code embedded in a file or program
Worms are self-contained and may spread autonomously

11.  A Virus is a hateful program that spreads using a
transmission technique that generally requires user
involvement, and always have a hateful target
 A worm on the other hand, has ability to self-spread,
and may or may not have nasty purpose.

12.  Capable of severely slow down the working of the
internet
 To unable us to build better defense systems
 To unable possible good application
 The worst is yet to come!

13.  Morris worm, 1988
◦ Infected about 6,000 machines
 10% of computers connected to the Internet
 Code Red worm, July 16 2001
◦ Infected more than 500,000 servers
◦ Caused ~ $2.6 Billion in damages,

14.  Mimili and Mimail.F are email
worms cover themselves as
an email from the PayPal on-
line payment service and try to
steal credit cards info.
 This method of fraud is known
phishing