This document discusses different types of computer viruses including file viruses, boot sector viruses, and partition table viruses. It explains that file viruses replace executable program code with malicious code, boot sector viruses substitute themselves for the bootstrap loader program to automatically load when the computer starts, and partition table viruses modify the partition table. It also provides examples of other types of viruses such as Trojan horses, worms, and stealth viruses. Finally, it states that antivirus software is used to identify and remove malicious software from computers.

1. File virus
Boot sector virus/
partition table
virus

2. 1. File virus
• The file virus affects executable programs
(.exe)
• It replaces a part of original code file with
a malicious code, thus destroying the file

3. 2. Boot sector virus
• The 1st sector of the outermost track in floppy disk
contained a small program known as bootstrap
loader program.
• when computer was switched on, this program
used to load OS from floppy disk to the main
memory of the computer.
• A boot sector virus substitutes itself for bootstrap
loader. Virus gets automatic loaded into main
memory.
• Once loaded it starts affecting all files on disk.

5. Examples of viruses

6. 1. Trojan Horse: damages files by merging
unwarranted program code with
authorized programs.
2. Worms: this program duplicates its own
code.
3. Salami techniques: robs small amount of
money from user account and user
remains unaware.
4. Eaves Dropping: allows a person to
observe some message transmitted to
other people.

7. 5. Wire tapping: it has special transmission path
to divert flow of data from original user to
unauthorized user.
6. Stealth virus: these virus avoids self detection
by antivirus.
7. Logic bombs: these cause computer to
malfunction.
8. Data diddling: performs unauthorized
modifications of data and user is not aware of
it.

8. Antivirus software are computer programs that
attempt to identify, neutralize or eliminate malicious
software.