I was in a world where I had created a redstone-automated quarry. I noticed a skeleton was getting in the way of my minecart tracks, so I did these three things:

/gamerule doMobSpawning false

Flew upward a bit

Pressed / (was going to do /kill @e[type=!Player])

My game froze for a solid minute, then my screen went black, and my computer restarted.
QUESTION: Is there a new Mojang developer? These actions seem pretty random, and they might have a virus written into them or something.