I use Avast! too and I love it. It found so many things that Norton totally missed and they were viruses that were common! Plus, it's totally free and updates as needed.

I think you need to go in and uninstall whatever program it was that you installed, download Avast!, let it scan your entire system, shut down and do another scan. It took a few times of doing that, but it got rid of everything and I have had no problems since.

Just remember that there are MANY programs that pop up saying something like, 'you may have spyware/malware on your computer. Click here to scan.' DON'T do it, they pop up in random websites and put numerous cookies, spyware, etc on your system. It is such a pain to remove that kind of stuff.

Good luck.