Whenever you have doubts that your computer might be infected with a virus or a trojan then head over to HouseCall from TrendMicro and perform a full scan of your Windows installation. Or download Panda's SafeDisk and boot from it to clean up your system.
If you do not have an antivirus program running on your machine (huh? :) then you must, and we mean YOU MUST install one. A free and good antivirus solution is Panda's Cloud Antivirus Free edition.
Avast's free edition used to work well but after the upgrade to version 8 it started consuming ridiculous amounts of memory and slowed down the test computer way too much, so thumbs down.
Solid Hosting Support