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