Computer viruses are called viruses since they share some of the traits and behaviors of biological viruses.  A computer virus passes from computer to computer similar to biological virus passes from person to person.

A computer virus is a program which attaches itself to, ovewrites or replaces another program in order to reproduce itself without the knowledge of the user.

Some viruses are harmless, and might be present for several years with no noticeable effect  while some viruses cause damage to data and files or atempt to destroy files and disks.

Kinds of Viruses

• File virus is known as parasitic virus that secretly attaches itself and infects  an innocent program.
• Boot-Sector Viruses is a virus that hides inthe boot sector that the moment the computer boot from a drive containing an infected media the virues copies itsef into the Random Access Memory (RAM).
• Multipartite Viruses hides in theboot sector and the file system. A smart virus is known as stealth polymorphic armored multipartite virus (SPAM virus).  A stealth virus hides itself from antivirus software.  Polymorphic virus changes it’s appearance each time it infects a file.  An armored virus protects itself againts anti-viruses.
• Macro Viruses hides in a little programs embedded in Microsoft Word and Excel documents and spreadsheets respectively.
• E-mail Worms a malicious program that comes as an e-mail attachment.
• Hoaxes are just an e-mail message and not a program that contains scarry wrong rumor and warns to pass the message to all of your friends.