spyware

In general, any software used to secretely extract information. It's most commonly used in reference to software that in addition to fulfilling its purpose sends private information to the company that created it. Even though this is frowned upon companies continue to attempt to harvest personal data using spyware.

How to get rid of spyware?

Spyware and spam are without a doubt the plague of the information age, but fortunately there are some more or less effective (depending on how up to date you keep the software) cures for the former: Ad-aware and Spybot.

Ad-aware can be found at: http://www.lavasoftusa.com/
Spybot at: http://security.kolla.de/

Disclaimer: I am not affiliated with those software developpers and I only give the URL to their websites here because they are totally free of use (except Ad-aware which has a "Pro" version, but you still don't lose any of the functions useful to a home-user on the free package).