I used to use the free anti-virus like Free AVG, Avast or Avira, but I’ve found that at some points as below:
1. In every version of AVG I’ve used – it stops updating automatically.
2. Most of the free anti-virus software don't have sufficient protection, especially on web surfing and thumb drive.
So a couple of months ago I decided to try another free Anti-Virus - Panda’s free Cloud Antivirus, and I'm happy with it for now. Updates happen in the background, files and problems are quietly taken care of, and it only ever bugs me if it needs my attention to decide what to do about a detected virus. Anyway, it only supporting Windows XP and Vista 32-bits.
AVG Anti-Virus Free edition is the most famous AV software.
It works well with Comodo Firewall, it's 100% free as well. If you manage to install and use both protection software for your PC/notebook, it will be getting perfect. Trust me.
Can Panda Cloud Anti-Virus take over AVG Free AV?
So what you waiting for? Try it today. Enjoy.