Understanding Windows Firewall
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
1. Click
Start and then click
Control Panel.
2. In the
Control Panel, click
Windows 
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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