Microsoft Security Essentials

Finally Microsoft has released free anti-virus software!!  This long over due free add-on to Microsoft Windows seams to work well. I have been using it since the Beta edition.  A few colleges and I have been running this software with good luck.  It doesn't seam to bog down your system and seems to work better then most free anti-virus.  No annoying pop ups, just good anti virus software.

http://www.microsoft.com/security_essentials/