Spyware is malicious software that monitors the activity on your computer - such as password details or the websites you have visited.

Spyware can use this ill-gotten information in lots of different ways, and could hijack your internet browser to show unwanted advertising or generally change your computer settings. It's designed with one purpose in mind - financial gain for the people who put it there.

Many anti-virus packages now come with built-in protection against spyware.

Windows Vista and Windows 7 come with integrated protection against spyware. If you use Windows XP, you can add this by downloading Windows Defender from the Microsoft website.