Why does a certain Web site now trigger a warning from my anti-virus when I never had a problem before?

I've been visiting this site for years (zap2it.com) and never had a problem, but for the last several weeks, every time I visit it, it triggers my MSSE anti-virus saying it is the cycbot.b virus. Good thing it is caught since I read up on this bug and it's a BAD one. What might have changed on the Web site to cause this? It makes me wary of ANY Web site now.