spyware

Spyware is a computer software installed on a computer without the owner knowledge in order to take partial control over it. Like the name suggests, the goal of spyware is to monitor the activities of the PC user, but it has other functions as well:

Different from computer viruses and worms, spyware doesn't self-replicate and usually it doesn't try to infect other systems. It exploits the security vulnerabilities of the PC for commercial benefit.

You can be infected by spyware in various ways. Spyware can be a payload of a worm, it can piggyback on legitimate software or you can be misled and be convinced to install it. Spyware is known to change computer settings resulting in slow connection speeds, switch in home pages and loss of Internet or functionality of other programs.