install malwarebyte's antimalware software and scan in safe mode using it.

ur machine is infected with some malware/spyware/virus.

did ur machine have any virus recently, i once had, internet security 2010 or sth like that...

http://answers.yahoo.com/question/index;_ylt=AjuBmMkgHEgGPxBVYH2khUAjzKIX;_ylv=3?qid=20091123105346AACfnFg

hope that helps.