Windows XP includes ICF, which allows you to protect a single computer, or the shared Internet connection (ICS) computer, if you are not already protected via a proxy or firewall.
To enable / disable ICF:
- Control Panel / Network Connections.
- Press the Dial-up, LAN or High-Speed Internet connection
that you want to protect press Change settings of this connection (under Network Tasks).
- Select the Advanced tab. Check or clear: