According to site advisor[tm] : Feedback from some users indicated this site engaged in one or more negative or undesired activities.
That's because you can get pop-unders from them. They give publishers full control of what ads to show down to individual ads (and by category as well, e.g. pop-unders off, flashing ads off). We of course disabled pop-unders, but they have them in the menu (with ecpm of around $10 btw).