Installed and Updated Avast Antivirus Professional

I just installed and updated Avast Antivirus Professional v4.8 since The Eset Smart Security Patch did not work. Avast do not provide firewall with its service hence I had to install ZoneAlarm Personal Firewall for that.
Now its ok and working proper for the time being.
I always end up with Avast after moving through a bunch of antivirus softwares I found that all the antivirus softwares are the same. It does not make any difference which software you are using since the response of the antivirus software is not the same while removing the viruses.
When I ended up being a victim of the avpo.exe\amvo.exe a pen drive virus which I got froma friends pen drive. I tried all the antivirus softwares but sice it was a worm and not a virus its removal became impossible in not only the avst antivirus but also other products too.
This made me realise that viruses can only be prevented from proper settings of the windows as well as taking careful precautions to see that there is no infection at all.