For those who didn't read about it, someone hacked AP and posted news about an attack on the Whitehouse forcing stocks to plummet for two minutes and then return to normal. Can't believe the market is vulnerable to tweets now.
Sometimes hacks like this are designed to move the markets. Back when Steve Jobs was alive, there was a group trying to hack AP to post a phony article that Steve Jobs had died - the purpose was to cause an immediate drop in Apple's stock, buy some, then sell it off before the day was over once it rebounded as news of the false report spread faster than the news of his phony death. Would have been an easy 15% one-day gain if it had been executed. I don't remember if they were stopped before doing it, or were just unsuccessful in executing, but I remember hearing about this at a tech networking event. Follow the money on things like this... if they look for unusual intraday transactions they might be able to find who was responsible.