The Associated Press has suspended its Twitter account after a “bogus” tweet was sent out about an attack on the White House
The tweet said that there had been two explosions at the White House and President Barack Obama was injured.
AP spokesman Paul Colford quickly confirmed the tweet was "bogus".
However, within three minutes of the tweet hitting the internet, virtually all US markets took a plunge on the false news in what one trader described as "pure chaos."
White House spokesman Jay Carney told reporters soon after the tweet went out around 6pm Irish time that Mr Obama was fine.
The attack on AP's Twitter account and AP mobile app was preceded by a phishing attempt on AP's corporate network.
AP confirmed that its two Twitter accounts, @AP and @AP--Mobile, had been suspended following a hack and said it was working to correct the issue.
It released the following statement: "The @AP twitter account has been hacked. The tweet about an attack at the White House is false. We will advise more as soon as possible."
It also later reported hackers had previously made repeated attempts to steal the passwords of AP journalists.
The tweet briefly sent the Dow Jones Industrial Average sharply lower.
It fell more than 150 points after the fake Twitter posting, then quickly recovered.
In what one trader described as "pure chaos," the three-minute plunge triggered by the tweet briefly wiped out $136.5 billion of the S&P 500 index's value, according to Reuters data.
It was the latest hacking incident involving news organisations.
On Saturday, social media accounts maintained by CBS News programmes "60 Minutes" and "48 Hours" were compromised.
A group calling itself the Syrian Electronic Army, which is supportive of President Bashar Al-Assad, claimed responsibility on its own Twitter feed for the hack.
The group has also claimed it was behind past hacks of Twitter accounts for National Public Radio, BBC and CBS's "60 Minutes", among others.
Earlier this year, hackers also hijacked Twitter accounts of Chrysler's Jeep brand and fast-food chain Burger King.