Stands for "Internet Connection Firewall." ICF is a Windows XP feature that protects computers connected to the Internet from unauthorized access. When ICF is enabled, Windows keeps a log of incoming requests from other systems on the Internet. If the request is something the user has requested, like a Web page, the transmission will not be affected. However, if the request is unsolicited and is not recognized by the system, the transmission will be dropped. This helps prevent intrusion by hackers or malicious software such as spyware.
While ICF limits incoming traffic from the Internet, it does not affect outgoing traffic. This means data sent from your computer is still vulnerable to viruses or other disruptions even when ICF is enabled. If you have multiple computers sharing the same Internet connection via ICS, you can enable ICF for all the computers. However, you should enable ICF for the router or system connected directly to the Internet connection, not for each individual system.