I just got a Security Tool pop up?!?!?!?

So I was on DeviantArt.com (no viruses) and I got one of those pop ups that say "you computer is infected!" I know this leeds to Security Tool because my sis had the exact same pop up to get the Virus. How did I get it? I have Limewire, is it from Limewire? Traker cookies? I need to know, my new computer might be at risk you guys!!!