I recently had a bad trojan on my personal computer (not that kind
) and neither AVG or Malwarebytes could get rid of it so out of an act of desperation I tried MS Security Essentials and it instantly found and removed it and I have not had a problem in weeks. Normally I would say don't waste your time with free ms av programs but they have my vote for now.
I still run AVG and use MB but MS Security Essentials is doing a good job catching things that AVG does not. As for Norton and McAfee. BLAH, don't waste your money on them when you can get better for free.