Opera Turbo is a feature of the Opera web browser. This feature uses Opera servers as proxy servers for the client. The Opera servers receive the contents of the webpage, compress it, and send it to the Opera browser to decompress and display the contents to the user.
Opera Turbo bypasses the ProxySG appliance's web filtering categorization feature; it disables explicit proxy functionality on the browser, allowing Opera to connect to Opera's caching servers.
In transparent proxy deployments, the ProxySG appliance blocks direct connections to Opera because they do not have a valid HTTP.
In explicit proxy deployments, the ProxySG appliance does not block connections to Opera. To block direct connections to Opera from your client computers, block connections to the subnets 126.96.36.199 through 188.8.131.52 on your firewall.