ICFShort for Internet Connection Firewall, a feature of the Windows XP operating system. The ICF is a firewall that protects a home or small business network that is connected to the Internet via a cable, DSL or dial-up modem. Devices that are connected to the Internet via a software or hardware router cannot use ICF.
Windows XP keeps a log of any information a user requests from the Internet -- for example, when the user requests a Web page or accesses an e-mail account. When information enters a computer, ICF checks the log to determine if it is something the user has requested. If ICF does not recognize the request, it drops the transmission and records the activity in a separate log that the user can check to see if any security issues need to be addressed.
ICF only blocks undesirable Internet traffic from coming into a network; it does not prevent outgoing traffic from being subjected to malicious hacker attacks such as Trojan horses or spyware programs.