Avast Detected When I've Never Installed It

Ok, I've been reading a lot of people talking about V5.00.5050 picking up Avast 6 and 8 because of remnants left over. However, mine's picking it up after I've never even installed an Avast product on this computer before. Needless to say, this both worries and perplexes me, and I'm thinking a dupe software might have installed registry keys there without my permission.



Any ideas?