Comodo Internet Security
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Full user review
"Great almost perfect"
It's a great free protection with a killer firewall, I mean nothing gets through at all. Scanner is decent too. Oh and don't forget it's free.
The scanner doesn't pick up tracking cookies and its update lags every once in a while.
If you want to protect your pc for free there is nothing better. The firewall makes up for the scanner, so use if you like.