Microsoft Security Essentials

Microsoft Security Essentials provides real-time protection for your home PC that guards against viruses, spyware, and other malicious software.
Microsoft Security Essentials is a free* download from Microsoft that is simple to install, easy to use, and always kept up to date so you can be assured your PC is protected by the latest technology.

http://www.microsoft.com/security_essentials/
Jens Meggers, vice president of engineering, Symantec said, "Microsoft has a really bad track record in security. Like OneCare, Security Essentials is a poor product." Microsoft's MSE team might be sharing high-fives on disturbing the competition to mock them.