Computer viruses are malicious codes/programs that cause damage to data and files on a system. Viruses can attack any part of a computer's software such as boot block, operating system, system areas, files and application-program-macros etc.
Two other similar ro rams also cause virus like effects. These are :
(a) Worms. A worm is a self-replicating program which eats up the entire disk space or memory. A worm keeps on creating its copies until all the disk space or memory is filled.
(b) Trojan Horses. A Trojan horse is a program that appears harmless (such as a text editor or a utility program) but actually performs malicious functions such as deleting or damaging files.
DAMAGE CAUSED BY VIRUSES
Viruses can do the following if left unchecked:
》Damage or delete files. Some viruses may delete or damage random documents or specific files that are crucial to your operating system—for example, operating system files. This damage can range from rendering useless just a few files to affecting your entire computer, possibly requiring you to reinstall your operating system and start from scratch.
》Slow down your computer. Viruses can run in the background, without being seen, and may cause your computer to run extremely slow.
》Invade your email program. Some forms of viruses may wreak even more havoc by spreading themselves to the contacts in your address book.