Spyware is small pieces of code that are put in someone's computer to secretly gather information about the user and relay it to advertisers or other interested parties.

Originally Spyware was for legitimate marketing purposes but has broadened into more insidious uses such as dialers which cause the computer to dial premium rate numbers and keyloggers which record keyboard typing and transmit this information to a third party.

Spyware is also the major cause of multiple pop-ups.

A computer virus attaches itself to a program or file so it can spread from one computer to another, leaving infections as it travels.

Much like human viruses, computer viruses can range in severity; some viruses cause only mildly annoying effects while others can damage your hardware, software, or files.