This document discusses computer viruses. It defines a virus as a program that infects and damages files. Viruses replicate by attaching themselves to other programs. They can be transmitted via email attachments, downloaded files, removable drives, or networks. Common symptoms of virus infection include computers running slowly, files changing or deleting unexpectedly, and error messages. The document recommends using antivirus software, scanning downloads, and avoiding suspicious websites or attachments to prevent virus infections. It describes two main types of viruses: boot sector viruses, which infect the boot sector and prevent computers from starting up, and file infecting viruses, which change the contents of files and replicate within files.

1. BY: Prabesh Shrestha

3.  It is the program which infects and
potentially damage the files in the computer
that receives it.
 It replicates and spreads by attaching itself
to other programs.
 A simple virus can make a copy of itself over
and over again.

4.  To take control of a computer and use it for
specific tasks
 To steal sensitive information (credit card
numbers, passwords, personal details, data
etc.)
 To prove that it can be done, to prove ones
skill
 For revenge purposes
 To cripple a computer or network
 For fun
 To earn fast money using malware

5.  From infected email attachments
 Downloading infected program from the
internet
 Using infected pen drives, CD, DVD etc.
 Transferring infected program over the
network and running it.
 Using pirated and illegal programs and
installing it into the computer
 Not having any updated antivirus programs to
control the virus infection

6.  Applications take longer time to load or may not
work at all
 Getting unusual error messages like Write Protect
Error
 Computer gets slow, freezes and crash some times.
 Important files or folders get changed or deleted
for no reason
 File size changes
 An increase in the number of files on the system
when nothing has been added
 Reformatting the hard disk
 Strange movements or patterns are seen on the
computer screen

7.  Use software from original CD or DVD.
 Do not use any pirated software as they may
contain virus.
 Use updated antivirus program.
 Always scan the downloaded files before
using them.
 Scan e-mail attachments before executing
them
 Do not use the removable disk such as pen
drives, floppy before scanning for virus
 Do not open any unknown and suspicious
websites or links.

8. 1) Boot Sector Virus
 It infects the first sector i.e. boot sector of the
hard disk or floppy disk.
 It can also infect MBR (Master Boot Record)
 It changes the instructions stored in the boot
sector
 It prevents the computer to turn on
 It works when we turn on or restart the
computer
 Eg: Disk Killer, Michelangelo, Stoned, Bouncing
Ball

9. 2) File Infecting Virus
 It infects the executable files having .exe,
.com, .drv, .sys, .ovl, .dll as extension name.
 It changes the contents of executable files.
 It replicates itself and infects files on the disk.
 It is spread by removable disks, through
network etc.
 It is easy to be detected because it changes the
size of the file.
 Eg: Friday the 13th, Enigma, Nemesis, Cascade
etc.

10.  It is a program designed to detect and
remove viruses from the computer system.
 It scans hard disk, removable disks, CD, DVD
etc.
 It needs to be updated regularly or from time
to time to ensure the smooth running of the
computer system.
 Eg: Norton antivirus, AVG, Kaspersky, Avast,
Avira, NOD32, Panda etc.

11.  It is a program that hides its purpose — it
claims to do one thing but really does
another
 It contains malicious or harmful codes which
can control and cause damage such as ruining
File Allocation Table(FAT) on hard disk.

13.  It is a malicious program which gets
transmitted by computer networks.
 Once it is installed it generates additional
email messages containing copies of the
worm.