Software firewalls are often less expensive and easier to configure than hardware firewalls.

Both Mac OS X and Windows XP include firewall software, at no extra charge.

Software firewalls also don't require you to move any cables around. Depending on the software you choose, a software firewall can offer features beyond those of router firewalls, such as protecting your computer from spyware (a component of some free software that tracks your Web browsing habits) and Trojan horses (a program that claims to do one thing, but does another, malicious thing, such as recording your passwords).

If you travel with a laptop, a software firewall is a necessity - you need protection wherever you connect to the Internet, and your hardware firewall can protect you only at home.

The firewalls which are bundled with Mac OS X and Windows XP are designed to provide basic intrusion prevention, but don't many of the rich features of a third party firewall application. Most third party protect you from software that may violate your privacy or allow an attacker to misuse your computer, features not found in the bundled firewall applications.

Please note that firewall software does not replace antivirus software. You should use both.

Popular software products include ZoneAlarm, Agnitum Outpost Firewall and Kerio Personal Firewall. Most personal firewall software is available in free or trial versions, so it won't cost you anything to download these products and determine if they meet your needs better than the bundled firewall.

Below is a list of some of the many firewall software packages available:

Zone Labs Firewall - requires Windows 98SE / Me / 2000 / XP

Outpost Firewall - requires Windows 95 / 98 / ME / NT / 2000 / XP

Kerio Personal Firewall - requires Windows 98 / NT / Me / 2000 / XP

Sygate Personal Firewall - requires Windows 95 / 98 / ME / NT / 2000 / XP

Brickhouse - requires Mac OS X 10.0 / 10.1

Intego NetBarrier - requires Mac OS 8.1 to 9.x / Mac OS X 10.1.1 or later

Firewalk - requires Mac OS X 10.1 or later