Member Rara Avis
Ads on the Internet cannot run programs on your computer unless you tell them they can, either by clicking a program (in which case you are asked to run or save the program) or by allowing Active-X controls. It's possible you have Active-X controls enabled, but not likely (at least no one should EVER have them enabled).
I hate to say it, but the most likely scenario is that you are infected and not being as fully cleaned as you might think. Otherwise, I would expect a lot more people to be experiencing the same (including me, since I use IE on the forums). Easy to check. Clean your system as you did before and then do NOT come into the forums. If you see the same thing on, say, Google, you can be sure your own system is the one requesting the programs to be loaded.
I'm a bit rushed for time right now, but will check into our advertisers a bit later to see if other sites have complained about nefarious behaviors.