What type of technique might be used by these offenders to access the Internet without restriction?

Neil is closely monitoring his firewall rules and logs on a regular basis. Some of the users have complained to Neil that there are a few employees who are visiting offensive web site during work hours, without any consideration for others. Neil knows that he has an up-to- date content filtering system and such access should not be authorized. What type of technique might be used by these offenders to access the Internet without restriction?

A.
They are using UDP that is always authorized at the firewall

B.
They are using an older version of Internet Explorer that allow them to bypass the proxy server

C.
They have been able to compromise the firewall, modify the rules, and give themselves proper access

D.
They are using tunneling software that allows them to communicate with protocols in a way it was not intended

Explanation:
This can be accomplished by, for example, tunneling the http traffic over SSH if you have a SSH server answering to your connection, you enable dynamic forwarding in the ssh client and configure Internet Explorer to use a SOCKS Proxy for network traffic.