Comodo Firewall has the worst reviews I'v read.
It's designed to be a Firewall in general and not an anti-virus.
There are many better programs that are free and do a better job than Comodo.
Like:
Microsoft Security Essentials
AVG Free 2012
Avast Home Edition 6
And if you want some strict security , you can try
Avira Anti-Vir
All of these free anti-virus programs are found to perform better then Comodo in the anti-virus business and I'll be glad to give links to the reviews if anyone wants them.