The free version of this personal firewall prevents hackers and virus to take control of your PC using the security flaws of Windows. It has a cool interface and many settings options : you can modify the filtering rules, give authorizations to some softwares, open ports...

 

Edited by Sunbelt, Kerio Personal Firewall runs in full mode for the first 30 days of use, then it switches to the free mode, for an unlimited time, in which some features are disabled.