What is a virus ? What is anti-virus software ?

A virus is a 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.

Anti-virus software is designed to detect and block attacks from malware. This software when loaded, resides in memory and checks every operation if it is malicious or not. If it finds any suspicious activity, it blocks that operation and saves our computer.