I worked as an operator on a BULL DPS 7 for a while back in the day. Everyone knew that the system engineers on site had the most powerful computers, but during the night we had the run of the place.
Somebody had put Lode Runner on one of the engineer's PC, and the night crew, while the tapes were turning, would take turns playing.
Somehow, he found out. He wasn't happy, but he didn't bother with an inquisition ; he just activated the BIOS password on his PC.
Night shifts were a lot more boring after that.