NEW YORK —
A group called the Syrian Electronic Army said it was responsible for the hack. But the claim has not been corroborated. The FBI and the Securities and Exchange Commission said they had opened investigations into the incident.
Some Wall Street pros were surprised that a single tweet could move markets so much.
Julian Brigden, managing partner of Macro Intelligence 2 Partners, an investment consultancy, said the drop suggested an "unstable" trading environment dominated by investors too quick to buy or sell without any thought.
"To me, it's indicative of a very dangerous market," he said.
Though stocks eventually recovered for the day, investors have been on edge recently.
"People are looking for a reason to sell, and (Tuesday) it was a fake tweet," said Adam Sussman, head of research at Tabb Group, a research firm. "Of course, once they realized it was fake, they bought back in, or they stopped selling."
But he thinks humans played only a minor role in the stock plunge. He said most professional investors are too savvy to sell on a tweet.
"They'd get a tweet from AP and then say, 'Oh, was there a corroborating tweet from Bloomberg? A corroborating tweet from Thomson Reuters?' and so forth," he said. "So I don't believe that anyone selling substantial money saw that tweet and just began selling off billions of dollars."
Joe Fox, founder of online brokerage Ditto Trade, said the selling was too fast for humans to have pulled off, and computers were to blame.
"Whoever this jerk (who wrote the tweet) is probably cost some people millions of dollars in a matter of minutes," he said.
Computer programs have come to dominate stock-market trading over the past 20 years. The goal is speed, and it's led to an arms race as companies develop ever-faster programs. High-speed trading came under public scrutiny following the "flash crash" of May 6, 2010, when a glitch erased 600 points from the Dow in five minutes.