A computer virus is a malicious code that is hidden in an apparently safe program and file. The virus loads itself to the computer without the knowledge of user and makes the computer to function in a way that is not facilitated by the authorized and legal owner or administrator of the computer.

Computer viruses are believed to be one of the most critical and harmful threats to computers and have the capability of inflicting serious damage to files, data and information stored in a computer. An antivirus detects and removes computer viruses.

The solution or remedy for this nightmare is an antivirus software. Antivirus software is designed to detect, block and then remove a virus. Antivirus programs use various techniques for detecting viruses. These include signature-based scanning, behavioral scanning and heuristics. Once detected, the antivirus software asks the user to perform appropriate action against the virus or selects a specific response from options like delete, repair or quarantine.

Spyware is a program that is engineered to steal valuable information from a computer. It works in stealth mode and is extremely difficult to detect and remove.

A computer program that is developed to detect and remove spyware programs is called anti-spyware. Anti-spyware programs are usually based on behavioral scanning methods that detect and remove spywares.

Spyware programs are also used for surveillance purposes even by state agencies and departments. Such spyware programs are sometimes flagged as 'safe' by anti-spyware software.

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