I've suddenly started getting pop-ups ALTHOUGH I have my pop-up blocker on. I've run Malarebytes, Microsoft Security Essentials, Microtrend and AVG, but no threats are found. What could be causing this? Thanks MUCH!What type of popups? When and where do you get them?

And do you have both MSE and AVG installed?Yes, I do have both MSE and AVG installed. However, I only installed AVG after MSE didn't find anything. The popups are occuring on a sweeps site (onlinesweepsstakes.com) which does not use popups. I double-checked to make sure it wasn't something that had just recently been started with them. And they're occurring on the sweeps site itself, not one of the individual sweeps (if that makes sense). Does this help? And should I now uninstall AVG?
You should NEVER use more than one anti-virus !!

Uninstall the one you dont want from 'Uninstall Program' in the CONTROL Panel1) Please uninstall one of the two AV's. You only want to have one av app installed.

2) Are you saying the pop up issue is only on that site? If so, it SOUNDS more like a site related problem than a browser or system issue.Check mark the block pop-up windows in firefox from tools->content tab

I. explorer
Privacy tab -> Turn-on pop-up blocker.I don't use Firefox ~ use IE9 ~ and have popups blocked. Thanks to all.