A personal firewall is a firewall-like software application which runs on a users PC.
Traditional software-based firewalls run as the only application on stand-alone computers which have been hardened to protect against hackers. Personal firewalls run on PC's along with all of the other applications required by the PC user.
Traditional firewalls protect entire networks. Personal firewalls are normally designed to protect only the PC upon which they are installed.
Because they run on the same computer as the other applications, personal firewalls have more information available to them than traditional network firewalls. The traditional network firewall knows whether the traffic is TCP, UDP, or ICMP. It knows what port number the traffic uses. It may know something about the protocol being utilized. It also knows the source and destination of the traffic. A personal firewall knows all of this, but also knows what software application is sending or receiving the traffic.
Most personal firewalls pop-up windows to notify the user about unknown network traffic. The user is then given the choice to allow or deny the traffic.
Personal Firewall Limitations
Because they run on the same computer as other applications, personal firewalls are vulnerable to being infected, modified, or disabled by any computer viruses, trojan horses, or network worms which are present in other applications on the PC.
Personal Firewalls
Windows XP ships with a basic personal firewall already integrated into the Operating System.
More comprehensive personal firewalls are available from many vendors, including: Agnitum, Deerfield, ISS, Kerio, McAfee, Normal, Sygate, Symantec, Tiny Software, and Zone Labs.
