When I was eighteen...
Other four guys and me were "hired" as IT "interns" in a medium sized company. The company's owner wanted to start an IT dept. and develop it's own software on the cheap. We were given access to a Pick multi-user system that used serial VT-100 compatible terminals, and left alone with it for a week, to 'learn the ropes' including both the OS and the programming language (Something called "DataBasic", which was, in short, a dialect of BASIC with some embedded SQL-like capacities).
The first thing that happened was that the intern sitting in the console nearest to the server thought it would be funny to disconnect the serial cables of other users at random intervals. It took the rest of us two frustrating hours or so to discover the trick, using a communications log file kept by the server.
That day, when leaving, I grabbed one of the system's manuals and took it home with me. Thanks to said manual I learned that the system allowed sending messages from one terminal to another, that said messages could use extended attributes (text colour, text width, any ASCII characters, etc.) and that such messages could be automated using the DataBasic language.
So the next day I made a very short and simple program that at intervals would send to the
fucker practical joker's terminal one of the following:
- A backspace once per minute.
- A carriage return once every three minutes.
- A clear screen once every five minutes.
- A disconnect control sequence every 10 minutes.
The first three sequences weren't recorded in any log, but I added some randomness to the fourth, as not to make the trick too obvious. I also sent all the messages using black text on a black background, so the victim couldn't see the messages.
The poor sod spent all the day swearing aloud while trying to troubleshoot his "technical issues" and later staring suspiciously at us for growing periods of time. 8^)
Miraculously, the next day, the issue "vanished by itself", which left the joker even more baffled.
Needles to say, the guy never tried one of his jokes on us again!.