A virus is a program created by programmers to infect the operation the computer system.
Virus also called perverse software is a program which knows how to copy itself and attaches itself to other program which further spread the infection.
Virus prevention and removable
If computer has a bootable hard disk, it is a prime target for virus attack. Depending on the kind of ROM BIOS on our computer, we might be able to alter the boot up sequence so drive A is not sought for a bootable and potentially infectious disk.
Different types of Virus
There are following types of virus categories.
1) Trojan Force
This is a program that appears to do something useful but actually delivers a harmful effect such as spreading itself VIA E-mail or deleting or damaging file.
A mailer is a type of worm that attaches itself to E-mail that a user sends.
3) Mass Mailer
A mass mailer is a type of worm that automatically sends itself to multiple addresses from a user E-mail address book.
This is a program that spreads by making copies of it.
5) Back Door
This program sends information back to its creator about the infected system.