Microsoft has publicly released it’s new “free” security suite.  It is free to those running a genuine copy of Windows 7, Vista or XP.

Run a Free PC Privacy Scan Now

I had used the public beta of this same software and found it to be quite easy to use, runs quietly in the background and does not take a lot of system resources like some larger security suites.

This suite is a good alternative to some of the other freeware security offerings and integrates well with Windows.

Have a look at the Microsoft Security Essentials website for more information:
http://www.microsoft.com/security_essentials/