I don't know how they have it set up, but the laziest way to block pages is to add them to /etc/hosts mapping them to 127.0.0.1 . If you do that in OS X and Web Sharing (apache) is enabled (and it might be on their machines, although I hear Mountain Lion got rid of it?), then navigating to http://blocksite.com/whatever.html will give a 404 unless the web sharing directory actually contains the file "whatever.html". So it's very likely a simple matter of a lazy configuration rather than a nefarious attempt to make you think that the blocked site doesn't exist (which, really, what would be the motivation there?).