In the past, I’ve tested most of the popular free anti-virus programs, the latest being Microsoft Security Essentials. This application leads the pack with realtime protection against viruses and spyware and with automatic updates. I found that it operates unobtrusively, using few system resources. System scans are relatively snappy (less than 10 minutes). Installation is quick, although Microsoft verifies Windows first. The interface is simple, offering few options. Most people won’t need to adjust any of them, except, perhaps the scan scheduling.
Another essential tool to defeat the nasties is Malwarebytes’ Anti-Malware. It is able to remove viruses and spyware that other programs can’t touch. Although the free version does not offer realtime protection or automatic updates, it is still handy to have when a bug slips past your primary anti-virus. This brute also does system scans in less than 10 minutes.
The final piece of my essential AV toolkit is Spybot Search and Destroy. It is the granddaddy of anti-spyware apps and it is showing its age. It offers realtime protection but no automatic updates. System scans normally take 15-20 minutes. A ton of options are available when in the Advanced mode.
I’ve had good results with the above three programs, but no program or group of programs can be 100% effective against all of the bugs on the web.
Download Microsoft Security Essentials HERE
Download Malwarebytes’ Anti-Malware HERE
Download Spybot Search and Destroy HERE
DUMMR.com 
thanks