PROXY SERVER

First go to start > run > type "regedit"
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings]
Change the value of "ProxyEnable" and set it to "1". Change the value of "ProxyServer" and set it to an IP address and port that is invalid on your network such as "10.0.0.1:5555" (i.e. "IP:Port").
By changing these settings Internet access will be disabled for any applications that rely of the Microsoft proxy server information such as Internet Explorer, Microsoft Office, Opera browser.
To stop users from modifying the proxy settings add these restrictions to disable changes to the Internet configuration.
Find or create the key below:
[HKEY_CURRENT_USER\Software\Policies\Microsoft\Internet Explorer\Control Panel]
Create two DWORD values named "Connection Settings" and "Connwiz Admin Lock" and set them both to "1".
To remove the restriction, set the proxy settings back to their original values and delete the policy values.