Hackers took control of the Associated Press Twitter account on Tuesday and sent a false tweet of two explosions in the White House that briefly shook U.S. stock markets.
AP spokesman Paul Colford told Reuters that the message, which also said U.S. President Barack Obama was injured, was "bogus" but did not immediately provide more details.
The AP's Twitter account was suspended shortly after the fake tweet. The news organization said the tweet came after hackers made repeated attempts to steal the passwords of AP journalists.
The false report briefly sent both the S&P 500 and Dow Jones Industrial Average sharply lower before they recovered.
White House spokesman Jay Carney told reporters soon after the tweet went out that Obama was fine.
It was the latest hacking incident involving news organizations. On Saturday, social media accounts maintained by CBS News programs "60 Minutes" and "48 Hours" were compromised.
An FBI representative had no immediate comment on the AP hacking incident. A spokesman for the Securities and Exchange Commission declined to comment.