Spybot - Search & Destroy can detect and remove spyware of different kinds from your computer. Spyware is a relatively new kind of threat that common anti-virus applications do not yet cover.
If SpyBot-S&D finds such modules, it can remove them - or replace them with empty dummies in case their host software won"t run with its bot removed. In most cases, the host still runs fine after removing the bot.
For a list of "supported" bots see the feature lists below. The Spybot-S&D interface is so easy, that updates just require replacing a file of about 80k in size. Those updates are distributed by my software mailinglist, at the authors page and are also available from inside the programs update section.
Another feature of Spybot S&D is the removal of usage tracks, which makes it more complicated for unknown spybots to transmit useful data. The list of last visited websites, opened files, started programs, cookies, all that and more can be cleaned. Supported are the three major browsers Internet Explorer, Netscape Communicator and Opera.