I think even bigger question is why are they still running mainframe? :/
I've heard people call the system case of their PCs a 'mainframe'. I wouldn't be surprised if the reporter or prison's P.R. spokesman meant the prison education network's server. -- Buckle Up. It makes it harder for the aliens to suck you out of your car.
If the statement from the Prison Spokesperson is true (closed education network with no possible access to the Internet or other prison systems) why was the teacher of the training class fired ?
I also find the "at the time of this incident" part of the quote amusing. Does that mean they suspended those security measures and the prison education network is now wide open ?
The quote of the Prison Spokesperson first confirms that there was an incident and then goes on to claim that it would have been impossible. That doesn't give it much credibility.
Of course we don't have any details. Perhaps there was something that the IT teacher did that bridged the closed education network to the rest of the prison ? -- Got some spare cpu cycles ? Join Team Helix or Team Starfire!