Open C:\Windows\System32\drivers\etc\Hosts in Notepad. Open a command prompt window and enter ping followed by the domain name you want to check, for example, ping pjpc.net. Append a line to the Hosts file consisting of the IP address revealed by the ping, a space, and the domain name, for instance, 18.104.22.168 pjpc.net . Add any more domains you want to allow (the POP3 or SMTP addresses used to access e-mail, for example). Save the Hosts file and close Notepad. Launch Network and Dial-up Connections from the Control Panel, right-click the connection through which you access the Internet, and select Properties. Select TCP/IP in the components list and click the Properties button. On the General tab, note any existing DNS numbers and store them somewhere safe. Those numbers will be essential if you want to undo this modification. Check the box Use the following DNS connections and enter invalid DNS lookup addresses for Preferred DNS Server and Alternate DNS server—you can use 22.214.171.124 and 126.96.36.199. Restart the system. Any program that attempts to access a domain not listed in the Hosts file will fail. Truly determined users can log on to a “blocked” domain by entering its IP address instead of the domain name (though they won’t be able to follow links). Still, this is a free solution and can be quite effective.