Re: It is very important to select your victim carefully,
My first proper job in IT was as a field engineer working on ancient Control Data machines at a large government site. One machine was a CDC3600, Seymore Crays first super computer circa 1965. Looking through the manuals it was found that an interrupt could start the machine from the stopped state (yes, mainframes of that era had a Stop key that brought the whole machine to a halt). So a little machine language program was written that set up a timer interrupt, but then kept resetting the timer in a tight loop. This was left running at the end of a maintenance period, the operator came along and, seeing that the machine was running hit the stop key to load the OS. The console typewriter immediately printed "F*ck off I'm busy" and the machine started again. After a few tries, he came to the engineers shack to complain.
Joke done time to end it. Unfortunately hitting Master Clear or Stop (or any other key) had no effect. Time to panic! As the machine had core memory, even switching it off wasn't going to help. Eventually we found that holding Stop and Master Clear down together for 5 seconds or so stopped the monster. Time to retreat to the shack and change the underwear.