If you have never heard of Grisoft or Free AVG, you really should check out this Tweaknews review.  Then I would suggest downloading it and giving it a try.  If you really like the free version, there is a version you can purchase for fairly cheap which gives you more options to get support from Grisoft.
“What if I told you that there was a free option on the internet that has all the benefits of a good antivirus without the performance decrease, and unlimited updates for one small price. How affordable is this small price? Well, think as affordable as you can possibly get. That’s right, it is free.”

Here is some more Tech News from around the web:

Tech Talk