How come you did not notice all the popups and viruses poping up with the ads. Even when you get their ad zone codes, the popups pop up.
I'll be honest and say I never noticed pop-ups on my website :S Maybe because my country (in south-eastern Europe) isn't interesting, but most of my visitors are from the US and EU and I see none of them complaining about malwares or pop-ups. I've taken their ads down. I don't want to risk my visitor's safety and my website's reputation
Yeah, that might be the reason and that's a good choice, because annoying popups and spyware can drive visitors off your site.