I subscribe to some of the PC Mechanic newsletters, which provide me with many good computing tips.  You may be able to use this one.

(An editor of the newsletter) currently has AVG Anti-Virus running on my computer.  After running it for a couple of months, I must say that it certainly does do its job in preventing all kinds of viruses (except for the cold I caught this morning).  The best part is that there is a free version with full functionality and effectiveness and it comes with free updates!  Just go install it today and scan your PC for current viral infections that should have been taken care of weeks ago. 

Link: http://www.download.com/AVG-Anti-Virus-Free-Edition/3000-2239_4-10342876.html?tag=lst-0-2