I've been using Free AVG for 5+ years now.....and I have never had a problem....Never got a virus...."knock on wood".
Free AVG is very simple to use and they update it daily.....
Correction, never got a virus or had a problem in the last 5 years THAT YOU KNOW OF! You very well may have a keylogger or a virus that is sitting in dormancy ready to attack at the press of a button by the hacker that created it. I'm just saying people, they threw slews of viruses at these things and only 1 or 2 picked them all up. Chances are you have something on your machine.