The firewall built into Windows starting with Windows XP Service Pack 2. Windows Firewall provides a stateful inspection of packets that accepts only responses to requests originated by the user. This prevents 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 valid requests that a stateful firewall will allow responses to. Windows Firewall superseded Internet Connection Firewall (ICF) and is turned on by default. See firewall and XP SP2.