Here is the Dow Jones Industrial Average today. Notice anything?
You don't need to be an ace market analyst to recognize that it's strange for the market to drop a hundred points, and then rise back up to exactly where it was before within ten minutes. What happened? This:That's a fake tweet from the real AP account, which was hacked. Another AP account clarified this point.
The (at)AP twitter account has been hacked. A tweet about an attack at the White House is false. We will advise on acct. status.
— AP Stylebook (@APStylebook) April 23, 2013
The incident shows two facts about the world we live in: one: everyone is hackable, and two: markets are volatile. Volatile enough to bounce all over the place on the strength of one tweet. It also shows that there are certain sources we trust implicitly, like AP and the New York Times. CNN used to be on that list, but that trust has slipped away from them. Or it should have, but had CNN sent the same tweet, it's likely the market would have freaked out just as much.
A weird side note to all of this: notice how the Dow Jones actually has an equally large surge at the beginning of the day, despite the lack of errant tweets? Here's the Dow Jones since Friday:
It's been doing that every Tuesday this year. I'm not a stocks guy, but maybe there is some money to be made on day-of-the-week speculating.