The AP says that a computerized selloff that may have been caused by a typo (the theory is that someone typed $16 billion when they meant $16 million) caused the biggest ever drop during a trading day. How could one typo result in such massive turmoil? The idea is that the erroneous trade triggered other computers to sell.
From the AP:
No one was sure what happened, other than automated orders were activated by erroneous trades. One possibility being investigated was that a trader accidentally placed an order to sell $16 billion, instead of $16 million, worth of futures, and that was enough to trigger sell orders across the market.
Those not accepting blame for the selloff include both the NYSE and the Nasdaq. The SEC issued a statement saying regulators were looking in to what happened. (After they are done downloading their porn, of course, but that goes without saying.)
Banking executives are blaming the inevitable robot apocalypse:
“I think the machines just took over. There’s not a lot of human interaction,” said Charlie Smith, chief investment officer at Fort Pitt Capital Group. “We’ve known that automated trading can run away from you, and I think that’s what we saw happen today.”