When hackers infiltrated the Associated Press’s Twitter account in 2013 and sent out a message claiming the White House had been hit by two explosions and President Obama was injured, the Dow Jones fell 143 points in a brief but widespread market panic. The tweet was deleted as soon as it appeared, but its momentary presence was enough to trigger both impulsive human behavior and the high-frequency trading algorithms now used throughout the markets, which “read” the news and perform trades in response in mere nanoseconds. One trader saw the Associated Press–induced flash crash as “a comment on
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