There is a debate in the UK whether prisoners should have the right to internet access, including social media sites like Facebook. From that debate comes the following way around normal prison internet security controls:
British prisoners are banned from using social networking sites like Facebook. Britain — unlike many European countries — bars almost all inmates from access to the Internet, except for educational purposes under supervision. But authorities acknowledge that some have used smuggled mobile phones to update their pages, or have gotten friends on the outside to do it for them.
This obviously works at almost any corporate entity too.