Links to Anti-Virus/Anti Worm (etc.) Sites
According to PC Magazine, "Panda Cloud Antivirus ... aims to head off disaster by pushing its malware detection activity into the cloud, eliminating the need for local signatures. ... It's a powerful defender against malware attacks--and it's free." I'm using it. (Very hot!)
http://www.cloudantivirus.com/
My recent experience shows that avast! is one of the best. The home edition is also free for non-comercial use. (Still hot - 1/2013)
http://www.avast.com/eng/download-avast-home.html
My past experience shows that AVG is also among the best. Recently rated tops by PC Magazine. Their free edition is for non-comercial home use. (Still hot - 1/2013)
http://free.avg.com/us-en/homepage
I've not used it personally, but I see that Avira is still at the top of most reviewer's list. But some users complain about popups and other self promotional advertising.
More Related Recommended Software
I use and recommend Spyware Blaster:
http://www.javacoolsoftware.com/spywareblaster.html
Spyware Blaster inoculates your web browser(s) against known malicious web sites. Download it, update it, activate protection, then your set. I recommend regular Windows users check for updates fairly often, at least monthly. Or you can pay for automatic updates.
I also use and recommend CCleaner: http://www.piriform.com/
Malicious software often embeds code in the Windows registry, one of the reasons that Windows is so vulnerable. CCleaner not only helps with Windows housekeeping, but also has an excellent registry backup and repair component.
But, for real security, I recommend users migrate to Linux (or Mac) machines.
See: http://distrowatch.com/, and pick one.
McAfee's home page
Symantec's (Norton) home page
The Virus Bulletin (information about viruses and anti-virus software)
Site debunking virus myths and computer security urban legends
Antivirus at About.com (formerly the Anit Virus Mining Co - now somewhat sold out to advertising)