Windows XP SP 2 users already have a built-in firewall. However it is limited to only inbound filtering. As a result, many users prefer to use a personal firewall to control outbound connections as well. In recent years, many of the freeware firewalls were either abandoned (Kerio 2) or companies that produced them were sold (Sygate) and many of the freeware offering are very old outdated products (Outpost Free). Comodo Firewall however bucks this trend.
Vista users have the option of just relying on their built-in firewall because it includes outbound filtering , though this is turned off by default.
Many personal firewalls, have moved towards incorporating HIPS features because this is the only way to defeat leak tests. Another option is to combine a solid basic personal firewall with a strong freeware HIPS.
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Use it at your own risk. Just because a program, book, document or service is listed here or has a good review does not mean that I endorse or approve of the program or of any of its contents. All the other standard disclaimers also apply.
Free Software Firewalls
Online Armor Free Edition
Online Armor Free is a Windows NT/2000/XP firewall with a built-in host instrusion prevention (HIPS) system. It also has a limited form of keylogger detection and includes protection against script/worm attacks. In addition, it features self-protection against tampering and termination attempts by malware. The current version of the firewall, at the time I write this, performed well in independent leak tests.
- Comodo Personal Firewall
Comodo Personal Firewall is a Windows 2000/XP firewall, that filters both inbound as well as outbound traffic.
Among its features are the ability to detect application hijacking attempts via its application and component behaviour monitor, self protection against termination attempts by malware, protection of your PC during startup, etc. Note: they require you to activate the firewall and supply your email address.
- PC Tools Firewall Plus
This is a free personal firewall for Windows that provides inbound and outbound filtering. The firewall allows you to create rudimentary application rules (only to allow or disallow an application) and rules for the packet filter (where you can configure the ports allowed, etc). You will need to supply your email address to get a free registration code to run the software after the trial period. (Scroll down to the bottom of the linked page to find the free firewall.)
- Filseclab Personal Firewall Professional Edition
This Windows firewall filters inbound and outbound traffic. You can configure which applications on your system is allowed to access the Internet, although by default, it automatically allows certain applications (such as those from the company itself, or those signed by Microsoft) outbound access without question.
GhostWall is a packet filtering firewall with low resource usage and latency. It works on both 32 bit and 64 bit Windows.
Guarddog is a firewall configuration utility for Linux iptables. It also lets you maintain and modify the firewall in place. It uses a "what is not explicitly allowed, is denied" philosophy. The software is released under the GNU GPL.
WIPFW is a packet filtering and accounting system for Windows. It is based on FreeBSD's IPFW.
- SoftPerfect Personal Firewall
SoftPerfect Personal Firewall is a rule-based Windows network firewall that filters IP and non-IP traffic, supports configurations for multiple network adaptors, has a learning mode and comes with a set of predefined rules.
- Jetico Personal Firewall
Jetico Personal Firewall is a Windows 98/ME/NT/2000/XP firewall that has network packet filters, network events filters (that allows you to block application level events) and process activity filters (that hopefully blocks application hijacking attempts where a trojan uses your browser to send information to the internet).
- Firestarter - Free Linux Firewall Tool
Firestarter is an easy-to-use free firewall tool for Linux that has a wizard that allows you to customize your firewall, a real-time firewall monitor that allows you to view intrusion attempts, a graphical interface that works under GNOME and KDE, and support for Linux kernels 2.4 and 2.6. For those who aren't brave enough to muck around with netfilter / iptables, Firestarter is one way to set up your system so that it is protected from intrusions.
- Sunbelt Personal Firewall (formerly Kerio Personal Firewall)
Sunbelt Personal Firewall is free for home use. It controls traffic from your computer to the Internet (thus useful for blocking spyware, adware, and other software that call home to the Internet behind your back) as well as traffic from the Internet to your computer. The program works as a trial for 30 days and then reverts to the free version after that. This is a Windows firewall.
ZoneAlarm is an easy to use and free personal firewall that is used by many people on the Internet. The free version allows you to decide which applications you can allow to access the Internet, but does not allow you to block specific IP addresses. (Look carefully before you click - the "basic PC protection" link is the one that is free.) This is a Windows firewall. If you want comprehensive protection for your computer, you might want to consider their commercial offering, ZoneAlarm Security Suite which includes a firewall as well as antivirus, antispyware, antitrojan, identity theft protection, phishing and spam blocker, etc.
- Sygate Personal Firewall
This firewall allows you to set policies regarding applications that may be allowed to access the Internet, trusted IP addresses, ports, protocols, etc. This is a Windows firewall. Warning: this firewall is no longer maintained. The link above points to a third party download site (Simtel) that loads pop-up windows.