Be careful!
There are a number of Rogue Anti Virus advertisements out there, some are very persistant and are hard to get rid off. One of them called itself Anit-Virus 2000 if I recall, a real PITA.
There is a software called Crap Cleaner you can download, they also have other software that you might find useful .It is free but they do request support via Pay Pal.
I have run AVG ( getting pricey) and am using Stopzilla and Vipre now. They to do a great job.