I never heard of them. I can see from the style they are not monitored or curated very well. One drug forum suggested underwear with pockets to help get drugs into concerts.
I found great add-on for firefox named No Script , i think it's used by like 1 000 000 users or so . It will block every java /spying stuff and pop-up that all these forums use nowdays , but it will make your browser very slow . You can right click it and choose which sites you trust and which you don't . Since i got that i never had issue with any virus from ads .