Comodo's free Firewall is your first layer of defense against viruses, worms, Trojans, hackers and all Internet threats. Comodo's Firewall uses Default Deny Protection to prevent threats from occurring, rather than just detecting them when it's already too late. Whenever an unknown piece of software is introduced to your system, Comodo Firewall cross-references it with a white-list of over 15 million trusted files and applications. If the file asking for access is on the list, Comodo Firewall can be sure it's safe for your computer to allow it to execute. If not, Comodo Firewall will alert you that a possibly malicious file is trying to enter your PC. From Comodo
Comodo Firewall's setup includes three network locations, with appropriate security levels for each: Home, Work, and Public. We chose Home. Comodo Firewall's operation is very much like other firewalls we've tried: the first time you use a program or access a Web site with the firewall running, you need to enable it in a pop-up that remembers your choice unless you tell it otherwise. The firewall's system tray icon accesses a menu that let us configure the Firewall and Defense & Security levels, and also its Sandbox feature and Game Mode.
