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.
Spybot-S&D is free, so there's no harm in trying to see if something snooped into your computer.
Download: Spybot Search and Destroy 1.4 RC
View: Spybot-S&D homepage