Quote Originally Posted by Lemur
I use Firefox, and I also use a lovely seconday script-blocking program called Spywareblaster. Despite these prophylactics, I get pop-ups in the Org from time to time. Quite irritating.
Spywareblaster is superb.

You could also try Adaware and Spybot S&D in conjunction with Spywareblaster and Firefox.

AVG is a good free anti-virus program.