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The new firewall in Windows XP Service Pack 2 is not by any means the most important security advance in the service pack. Other changes, principally locking down the My Computer zone in Internet Explorer, will have more profound implications for security of the average system. But it’s not unimportant.

Had Microsoft done the Internet Connection Firewall in the initial Windows XP this way—that is more aggressive, less troublesome for normal networking uses, and on by default—it would have prevented a lot of the damage caused by Blaster, Sasser, Slammer and some lesser attacks. Microsoft pointed out at the time that users who ran ICF were safe from those attacks, but that missed the point: Why would anyone run ICF when it interfered with the ability to do many normal networking operations?

Windows Firewall, as the new ICF is known, is a much better program. I’ve been running it for months now, and it hasn’t interfered with anything. In fact, I’ve barely noticed it. You may already have realized that this is a clue to some of the problems with it.

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It was important for Microsoft to build a firewall that didn’t hassle users with a lot of messages that would redound to their beloved OEMs and Internet service providers as support calls. Unfortunately, to do that, they made a firewall that’s very conservative about blocking potentially suspicious traffic.

For instance, with very few exceptions, Windows Firewall monitors and blocks no outbound traffic. Outbound monitoring is actually (mixing a couple metaphors here) like locking the henhouse after the fox is already in. A user who infects himself with MyDoom might be stopped from being part of a DDOS attack on by outbound monitoring. Windows Firewall doesn’t do this (how’s that for irony?).

There are still plenty of problems you might have with a default configuration of Windows Firewall. If you are running a game server of some kind or an uncommon chat program, you might need to accept incoming connections on a nonstandard port. For this, Windows Firewall lets you set a program and port “exception.”

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  • Windows Firewall trusts all systems on the local subnet. If you are on a hotel network or a public wireless network or an insecure cable modem network, you can be attacked by a neighboring system.
  • Many attacks, including Trojan horses, spyware and adware, don’t need inbound communications before they infect the system and begin unmonitored outbound communications.
  • Windows Firewall is a user mode application, and firewall vendors claim it is not as hardened as their products. Many viruses attempt to shut down security software, which must attempt to protect itself against the possibility. Windows Firewall is too easy to shut down.

Clearly Microsoft had to be dragged to the point of providing a decent personal firewall. They and we, the press, are in a tricky position of describing the benefits of Windows Firewall without diminishing the need for third-party solutions. It would be a shame if users got a false impression of just how much better Windows Firewall is.

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