By default, the free service that anyone can use, they redirect nonexistent domains to a search page they control. If you pay (and register your IP address), you can turn that off. But the main reason for paying is to control which domains are blocked. You can choose categories, and/or maintain your own white or black list. http://www.opendns.com/web-filtering/ and http://www.opendns.com/internet-security/