This is interesting.
Last week's meltdown of the UK's National Air Traffic Services caused the cancellation of more than 2,000 flights. The blame is being laid on a single military aircraft entering “spurious” flight data into the system.
"A flight plan submitted by a UK military aircraft caused a meltdown in air traffic control systems used by Nats which remained unfixed for several hours."
WTF?
There was no backup because backing up the amount of data involved was apparently too costly. (Ahem!)