Re: One wonders ...
0) The so-called "hack" and ElReg's fixation on laughing at the continuing use of PDP11s are, in all likelihood, completely unrelated.
1) The so-called "hack" is unknown. Could be as simple as picking the lock to the machine-room door or using a little social engineering on an employee at a pub.
2) The PDP11s in question can run realtime, multiuser, multitasking operating systems (probably). Whoever has access to the monitor/kernel can do pretty much whatever they like. Not that I would recommend it in such a scenario.