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ICF(Internet Connection Firewall) The built-in firewall in Windows XP. It provides a stateful inspection of packets which accepts only responses to requests originated by the user. This will prevent outside requests for data from entering the computer, unless specifically allowed by the user. However, spyware programs are often clandestinely installed in a user's computer which then make seemingly legitimate requests that a stateful firewall will allow responses to.
To turn on ICF, go to the Network Connections control panel and right click the connection (on the right side) that you want to protect. Select Properties, then the Advanced tab and check "Protect my computer..."
In the 2004 release of Service Pack 2 for Windows XP, Microsoft enhanced ICF and renamed it Windows Firewall. Unlike ICF, Windows Firewall is turned on by default. See firewall. See also IFC.