well, they are not viruses or backdoors, but they could contain spyware, i dont install nor see any of it, and honeslty, the advertisement is needed as it is how duffman supports his site, unless someone starts chucking cash his way to pay for all his services :P
If you have proper setup of your browser, you wont need to worry about popups. I use IE and don't even have probs. Enable popup blocking.
Else, Use Firefox or Opera