Good point about the AI that might find ways that humans didn't think of. But that would mean that Moore's law of Mad Science only now becomes true, and the drop would be steeper.

Still I think that even a super smart AI can't find a way to destroy the world without physical resources that are not easy to get, unless it can hack many systems (like in the movie Eagle Eye), maybe then yes. So let's use AI now to tighten security :-).