Korsa

Okay, my brother downloaded a Keygen on my computer, and its done something quite annoying. It keeps popping up every few minutes, just a little screen saying 'Keygen,' usually after I recieve a popup from Windows saying 'Firefox has stopped working.' I click Close Programme, and the Keygen pops up. I have NOT installed it, it is just a downloaded file on my Computer which I have deleted, and yet it is still popping up.. Any suggestions please?? :confused: Thanks Ollie.