Windows Firewall, previously known as Internet Connection Firewall or ICF, is a protective boundary that monitors and restricts information that travels between your computer and a network or the Internet. This provides a line of defense against someone who might try to access your computer from outside the Windows Firewall without your permission.

If you're running Windows XP Service Pack 2 (SP2), Windows Firewall is turned on by default. However, some computer manufacturers and network administrators might turn it off.

To open Windows Firewall

 

Security Center

 

Note You do not have to use Windows Firewall—you can install and run any firewall that you choose. Evaluate the features of other firewalls and then decide which firewall best meets your needs. If you choose to install and run another firewall, turn off Windows Firewall.

How Windows Firewall Works

When someone on the Internet or on a network tries to connect to your computer, we call that attempt an "unsolicited request." When your computer gets an unsolicited request, Windows Firewall blocks the connection. If you run a program such as an instant messaging program or a multiplayer network game that needs to receive information from the Internet or a network, the firewall asks if you want to block or unblock (allow) the connection. You should see a window like the one below.

 

Firewall security alert

 

If you choose to unblock the connection, Windows Firewall creates an exception so that the firewall won't bother you when that program needs to receive information in the future. To learn more about exceptions, see the Using the Exceptions Tab section of this article.

Tip Although you can turn off Windows Firewall for specific Internet and network connections, doing this increases the risk to your computer's security.

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What Windows Firewall Does and Does Not Do

If you're running Windows XP Service Pack 2 (SP2) the new Windows Firewall is turned on by default. To help protect your computer against viruses or security threats, we recommend that you keep Windows Firewall on.

Because a firewall restricts communication between your computer and the Internet, you might need to adjust settings for some programs that prefer an open connection. These adjustments are called "exceptions." To learn more about exceptions, see the Using the Exceptions Tab section of this article.

Windows Firewall now has three settings: On, On with no exceptions, and Off.

On: Windows Firewall is turned on by default, and normally you should leave it that way. When you choose this setting, Windows Firewall blocks all unsolicited requests to connect to your computer, except for requests to programs or services selected on the Exceptions tab.

On with no exceptions: When you select the Don't allow exceptions check box, Windows Firewall blocks all unsolicited requests to connect to your computer, including requests to programs or services selected on the Exceptions tab. Use this setting when you need maximum protection for your computer, such as when you connect to a public network in a hotel or airport, or when a dangerous virus or worm is spreading over the Internet.

Tip There is no need to keep Don't allow exceptions selected all the time, because when it is, some of your programs might not work correctly, and the following services are blocked from accepting unsolicited requests:

Note When you select Don't allow exceptions, you can still send and receive e-mail, use an instant messaging program, or view most Web pages.

Off: This setting turns Windows Firewall off. When you choose this setting, your computer is much more vulnerable to harm from unknown intruders or viruses from the Internet. This setting should only be used by advanced users for computer administration purposes, or if your computer is protected by another firewall.

To adjust Windows Firewall settings

 

Windows Firewall General tab

 

Note Settings that you create when your computer is joined to a domain are stored separately from those created when your computer is not joined to a domain. These separate groups of settings are called profiles.