Could be a virus similar to this one:
http://www.gnutellaforums.com/showthread.php?t=41432
Try any of these programs to scan your system (I reckon using all of them):
http://www.lavasoftusa.com/software/adaware/(free)

http://www.grisoft.com(good free AVG)

http://www.ewido.com(free trial which can still be used and updated after the period has ended -the best in my opinion)

http://www.ccleaner.com/download/(free)

Spybot - Search & Destroy (FREE)

If you can't get rid of it go here and get some free computer help:
http://norbiesworld.co.uk/computerhelp

__________________

"Never Argue With An Idiot. They Will Drag You Down To Their Level, Then Beat You With Experience"