Skynet
The UK government tempt fate once again, as they launched their second Skynet satellite on Friday.
As we all know from the Terminator movies, Skynet will at some point in the near future become sentient and take over all our computers, before unleashing wave after wave of robots to kill all humanity.
So prepare your shelter now, while we still have time.
Source: The Register
(Edit: Okay, okay, the Skynet program has been going since 1969, as pointed out by a comment on The Register, which does make it less funny.)