How could a fake tweet about an attack on the White House trigger a stock market slide?
It happened just over one year ago on April 23, 2013.
Someone broke into the Associated Press' Twitter account and sent out a false headline about explosions at the White House. Almost immediately, the Dow plunged and then rebounded as it became clear there had been no attack.
Here's CNBC's Courtney Reagan with a "Heat Map Time-Lapse" look back at that day and the questions it raised about computers triggering trading programs.