This document provides information about computer viruses and anti-virus software. It defines what a virus is, how viruses infect computers, the types of damage viruses can cause, and examples of common virus types, including parasitic, boot sector, stealth, macro, email, Trojan horse, and malware viruses. It also discusses precautions users should take to prevent virus infections. Finally, it defines anti-virus software as programs that scan for and eliminate viruses using virus signatures or by identifying suspicious program behavior, and discusses two main types of anti-virus programs.

1. VIRUS & ANTI-VIRUS
 TOPICS
 VIRUSES
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WHAT IS VIRUS?
HOW IT INFECTS THE COMPUTER?
WHAT DOES A VIRUS DO?
EXAMPLES OF VIRUSES
WHAT PRECAUTIONS SHOULD BE TAKEN?
 ANTIVIRUS
 WHAT IS ANTIVIRUS SOFTWARE?
 EXAMPLES OF ANTIVIRUS.

2. VIRUS
 Viruses are written by computer
criminals.
 Virus authors exploit not cleverness but
rather trust.
 Most viruses attack PC's via ports that
exist because of trust in the computer
community.

3. TOPIC 1- WHAT IS A VIRUS?
 Virus is the generic term that people are
using these days to describe any of
group of willfully destructive computer
programs. A virus is just a worm with a
logic bomb or Trojan horse component.
 Virus is a malicious software program
designed to harm computer programs.
 Virus means vital information on
resources under siege.

4. TOPIC 2- HOW IT INFECTS THE
COMPUTER?
A simple virus might work in the following way.
 1. The virus is introduced to your system either with an
infected .COM or .EXE file, or you boot from a floppy
with an infected boot record. This Trojan is either hidden
in an application program that has been doctored by the
virus creator, or it is the Trojan portion of a virus that is
injected into a program file or the boot record by the
worm portion.
 2. Once the program with the Trojan is activated, the
virus is awakened. It installs itself in the operating
system as a logic bomb, waiting for an opportunity to
(1) activate the worm and/or (2) activate the destructive
portion itself.

5. TOPIC 2- HOW IT INFECTS THE
COMPUTER?
 3. The logic bomb activates the worm portion whenever an
acceptable host presents itself. Some viruses only replicate
onto floppies from the hard disk. Other viruses infect any
program file that gets activated, whether on the floppy disk or
the hard disk, every time the worm copies itself onto another
disk or program, it activates a built-in counter that keeps track
of how many copies it has made.
 4. Eventually, the destructive part of the virus may be
activated, either by an event, like a program, a date occurring
or by a certain number of replications. When the destructive
portion activates, the virus may do something as innocuous as
flashing a message on the screen or as erasing the hard disk. I
say "may be activated," because some "viruses" are just pure
worms-no dangerous part, except for the annoyance of their
propagation.

6. TOPIC 3- What does a virus do?
Virus will infect the system in following ways
 Programs used daily are beginning to run more slowly
 Disk access appears ill-timed or more frequent than normal.
 Program load time increases, not just at peak usage times.
 The microcomputer locks up. Normal lock up is from power,
sloppy programs, or hardware incompatibility.
 Hardware and software problems appear after something new
is added to the system.
 Unusual or humorous error messages appear.
 Free disk space decreases dramatically.
 Memory-resident programs execute incorrectly or not at all.

7. TOPIC 4-TYPES OF VIRUSES
Parasitic Viruses or Program Infectors
 Parasitic viruses begin their dirty work whenever the
executable file to which they are attached is run. They hide in
the memory for just the right moment. They are also called
program inferiors.
 Another strain of program infectors is made up of two spilt
programs: one to be the top program that will not register as
a virus when a virus scanner runs, and one that contains an
algorithm that, once the first program is resident, changes
part of the first program's code to make it a virus. It's sort of
like a terrorist who gets through the security checkpoints at
the airport, apparently unarmed, and then converts his
umbrella to a shotgun once he's on the plane.

8. TOPIC 4-TYPES OF VIRUSES
Boot Sector Viruses
 Boot sector viruses generally prefer hard drives; a minority,
including the "Stonded" virus, infects floppies. They are loaded
into memory when the PC is booted from a drive which
contains an infected disk. You're probably wondering, "What if
the diskette is not really bootable (i.e. it has no
COMMAND.COM file) and the screen displays the message Non
system disk error?" That doesn't stop anything, unfortunately.
Once the computer boots from the infected disk, it's too latethe PC had to read the boot sector of the floppy to know it
wasn't bootable. During the read, the virus woke up and
sprang into action.

9. TOPIC 4-TYPES OF VIRUSES
Stealth Viruses
 Some viruses are said to be "stealth" viruses. A
stealth virus attempts to hide itself by keeping a
copy of the parts of the disk that it infected, before
it infected it. Then, when it detects that a virus
scanner is looking for it, it shows the scanner the
uninfected copy of the file.

10. TOPIC 4-TYPES OF VIRUSES
Macro Viruses
 One way of covertly introducing viruses into a computer is
through the use of a MACRO. A macro consists of several
instructions grouped together which then carry out a series of
instructions. Macros are normally very useful tools, that make
working with computer programs easier.
Common examples macro functions are: automatically
inserting the date and time into your document, displaying a
picture in your document, adding a sound to your document,
or automatically calculating something in a spreadsheet. To
perform these functions, the computer has to follow quite a
set of complicated instructions. These are called macros.

11. TOPIC 4-TYPES OF VIRUSES
Trojan Horses
 we define a Trojan Horse as a computer file or
program which seems to be useful, needed, or
wanted, but which is, in actual fact, a harmful file or
program. A Trojan horse looks like it is doing
something innocent, such as showing a picture
inside an e-mail or installing a screen saver. But in
fact it is also doing something else - such as erasing
files, or secretly sending information stored on your
computer (such as passwords and other personal
information) to the hacker who wrote it.

12. TOPIC 4-TYPES OF VIRUSES
Email Viruses
 An email virus is a virus that is distributed through
the use of emails, most frequently as an attachment
to an email.
 When the unsuspecting recipient opens the
attachment to the email, the virus is released onto
his or her computer. Most email viruses consist of a
macro virus that enters the address book on your
computer and then spreads itself to all of your
contacts.

13. TOPIC 4-TYPES OF VIRUSES
Adware - or Advertising-Supported Software
 Adware, which is short for “Advertising-Supported
Software” is any software which automatically plays,
displays, or downloads advertising material to a
computer after the software is installed on it.
It is usually included with other software
downloaded from the Internet, especially what you
download for "free". The price you pay is having the
adware installed on your computer. when you run
the program that you downloaded for "free" from
the Internet, it will usually automatically cause adds
to pop up on your screen thereafter.

14. TOPIC 4-TYPES OF VIRUSES
Malware
 Harmful software is also referred to as "malicious software."
"Malicious" means "intending to cause harm" and comes from
the Latin word "malus," which means "bad." The term
"malicious software" has also been shortened to the term
"malware." One can define "malware" as "software that is bad
or causes harm."
In earlier times, the only way to give a computer a virus, was
by inserting an infected floppy disk into your computer. Today,
with much more advanced technology, almost every computer
is interconnected to the rest of the world, one way or the
other. On top of all this, advancement in software and
computers have also opened the door to new types of
malware.

15. TOPIC 4-TYPES OF VIRUSES
Spyware
 Spyware another form of malware, which does
exactly what its name implies. It spies on you
through the use of your computer. Twenty years
ago only a subject of science fiction, it is today a
hard reality.
Spyware consists of a computer program that collect
personal information or other data stored on your
computer, and then sends it to the originator of the
spyware.

16. TOPIC 5-WHAT PRECAUTIONS
SHOULD BE TAKEN?
Virus protection amounts to common sense computer practice
 Backup the system regularly, since some viruses lay dormant
for weeks, months, or even years before activation.
 Purchase a good virus checker which includes scanners that
check files for known signatures and monitors that check DOS
calls. The checker compares programs by taking snapshots of
the disk to use for comparison.
 Do not download programs from bulletin boards directly to a
network station. Do this only to stand-alone computers.
 Do not buy software from unusual vendors, use only
government approved sources.
 Make the .com and .exe files read only files.

17. TOPIC 5-WHAT PRECAUTIONS
SHOULD BE TAKEN?
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Teach network users why they must comply with policies
regarding file transfer.
TrackLAN users who have more difficulty than others and
those who abuse the system.
Do not let support people use viruses as a convenient excuse
for every problem.
Establish a policy that an observation of irregular behaviour
should be reported immediately to a central network authority
and overlooked. Let a network professional decide whether a
problem exists or not. If a virus is detected, all near by
computers at risk should be checked as well. To minimize
infections, early reporting should be strongly encouraged.

18. TOPIC 6-WHAT IS ANTIVIRUS
SOFTWARE PROGRAM
 An anti-virus software program is a computer program
that can be used to scan files to identify and eliminate
computer viruses and other malicious software
(malware).
 Anti-virus software typically uses two different
techniques to accomplish this:
 Examining files to look for known viruses by means of a
virus dictionary
 Identifying suspicious behavior from any computer
program which might indicate infection

19. TOPIC 7- TYPES OF
ANTIVIRUS PROGRAMS
 There are two types of anti virus programs. Both do
more or less the same thing, but use different
methods. Both types of programs are constantly on
the lookout for viruses on your computer, but they
do so in different ways.
1. The first one keeps a list of known viruses and virus
types, called "virus definitions." This list of virus
definitions is called a virus library. It constantly looks
through your computer, checking to see if anything
coming into your computer is a virus. It does so by
comparing all things coming in with what it has
stored in its "virus library".

20. TOPIC 7- TYPES OF
ANTIVIRUS PROGRAMS
 Any file, document, or program coming into your
computer is inspected and compared to this library to
see if it matches any of the "virus definitions." One
disadvantage of this system is that if a new virus
comes out that is different than the viruses stored in
your library, this type of antivirus program will not
detect it and will allow it onto your computer.
 When using such a program, it is important to have a
subscription, and to be connected to the Internet, so
that your virus definitions are constantly updated.
New viruses come out every day. If you choose such
a program, one of the things to check for is how
often the virus definitions are updated. This will play
an important role in keeping your computer safe.

21. TOPIC 7- TYPES OF
ANTIVIRUS PROGRAMS
2. The second type of anti-virus program is called a
HEURISTIC program. "Heuristic" means "learning by
discovery or trail and error." It comes from the Greek
word "heuriskin," which means "to discover".
 In other words, the program is capable of discovering
new viruses not already known. It is written in such
a way that it is able to learn and discover new
viruses, without having to refer to a library. This
program will most likely also have a library of virus
definitions. But in addition to detecting already
known viruses, it is able to detect new viruses, and is
therefore a more secure program.

22. TOPIC 7- TYPES OF
ANTIVIRUS PROGRAMS
Some of the common Antivirus programs are as follows:
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Kaspersky Antivirus

AVG Free Anti-Virus
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Panda Software Anti-Virus Products
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Trend Micro
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McAfee

Panda Software Anti-Virus Products
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Kaspersky Antivirus and Internet Security
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AVG Free Anti-Virus and Internet Security
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Lava soft
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Panda Software Anti-Virus Products
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Trend Micro
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Norton Antivirus
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McAfee
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Trend Micro