Download the Best Free Firewalls: PrivateFirewall, Comodo, ZoneAlarm
A firewall controls the door to your computer and allows only traffic you understand and initiate.
PrivateFirewall is small, simple, light, surprisingly easy to use, and compatible with all Windows versions. It features, advanced packet filtering (blocking all unauthorized traffic), application control, process detection that prevents viruses, trojans, worms and other malware by tracking all trusted processes and providing alerts when any potentially malicious process attempts to run, an anti-logger module, system anomaly detection (normal use patterns of running applications are monitored and alerts are generated as unusual activity is detected), stealth mode, port tracking, email anomaly detection (tracking the volume and frequency of outbound emails). Privatefirewall conveniently detects connections to local networks and automatically sets rules that allow access within that network. I had nothing at all to do in order for eMule to keep using its special ports to enjoy high-id connection. I consider this a very special firewall, and I recommend it absolutely.
Comodo Firewall constantly monitors and defends your PC from Internet attacks. It’s easy to install and use and passes the industry’s most stringent firewall “leak” tests. However, there have been reported from time to time deficiencies, such as 100% CPU use by Comodo’s agent (cmdagent). Of course this may change according to version, and Comodo remains one of the best choices for a free firewall. Note also that it may prove difficult to ‘train’ Comodo let some applications enjoy special connection priviliges. For example, I had a lot of trouble trying to achieve high-id connection with eMule, until finally I removed Comodo Firewall and installed PrivateFirewall.
ZoneAlarm Firewall protects your DSL or cable-connected PC from hackers. This program includes four interlocking security services: a firewall, an application control, an Internet lock, and Zones. The Internet lock blocks Internet traffic while your computer is unattended or while you’re not using the Internet, and it can be activated automatically with your computer’s screensaver or after a set period of inactivity. Zones monitor all activity on your computer and alert you when a new application attempts to access the Internet. Note that ZoneAlarm may have problems with p2p sharing application, such as eMule. Besides this ZoneAlarm will leave its toolbar after you uninstall it (search for the guid EE2AC4E5-B0B0-4EC6-88A9-BCA1A32AB107 at the Registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Toolbar in order to remove “Zone Alarm security engine” from Explorer’s options). I don’t like this intrusive behavior and I don’t use ZoneAlarm.