re-install whatever OS you are running...otherwise run spyware, adware, virus proggies and hope for the best. i usually re-install at least once every 1 1/2- 2 years just to get rid of any random crap that might be getting by any scanning programs i run. if ur lookin for free programs try avg for virus scanner, i use spybot
http://www.download.com/Spybot-Searc...ml?tag=lst-0-1, and adaware for spyware and stuff.