http://blogs.technet.com/david_bennett/archive/2007/01/29/http-extension-for-windows-parental-controls.aspxTo make Windows Parental Controls work better with browsers and other programs that support http, the filter in vista sends back a custom error number when the page is blocked. This number is 450, an app can recognise this error code and display a blockeden-USCommunityServer 2.1 SP1 (Build: 61025.2)