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 sent US financial markets reeling.
In the latest high-profile hacking incident involving social media service Twitter, an official @AP account reported that two explosions at the White House injured President Barack Obama.
AP spokesman Paul Colford quickly confirmed the tweet was "bogus," but within 3 minutes of the tweet hitting the Web, 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 that Obama was fine soon after the tweet went out a little after 1 p.m. EDT (1700 GMT).
Markets quickly recovered their losses after the tweet was knocked down. Some traders blamed automatic electronic trading for the sharp fall and bounce back.
At a time when cybersecurity and hacking have become top national security concerns, Twitter and its reach to hundreds of millions of users is coming under growing scrutiny for the risk of data breaches on the site.
A group calling itself the Syrian Electronic Army, which is supportive of that country's leader, President Bashar al-Assad, during the two-year civil war, on Tuesday claimed responsibility on its own Twitter feed for the AP hack.
The group, which creates new Twitter accounts every time the company suspends its old ones, has recently also claimed credit for similar hacks of Twitter accounts for National Public Radio, BBC and CBS's "60 Minutes" program, among others.
The AP's two Twitter accounts, @AP and @AP_Mobile, were suspended shortly after the fake tweet, and the news organization later reported hackers had previously made repeated attempts to steal the passwords of AP journalists.
A Twitter spokesman declined to comment on the AP breach, saying the company does not comment "on individual accounts for privacy and security reasons." An FBI representative had no immediate comment on the AP hacking incident.
The spate of recent hacks have again turned the spotlight on what critics deem to be Twitter's thin security offerings. For years, security experts have called on the San Francisco company to introduce a measure called two-factor authentication that they say would greatly reduce such breaches.
In recent months, Twitter has appeared to respond by hiring security experts and posting job listings for software engineers who could help the company roll out two-factor authentication.
The false "BREAKING" tweet, which went out to the AP's nearly 2 million Twitter followers, sent the S&P 500 and Dow Jones Industrial Average falling sharply before they recovered. Stock and bond futures also were affected.
The three-minute plunge triggered by the tweet briefly wiped out US$136.5 billion of the S&P 500 index's value, according to Reuters data. The Dow Jones Industrial Average temporarily dropped 143.5 points, or 0.98 percent.
For a graph of the S&P plunge, see: link.reuters.com/gez57t.
A spokesman for the Securities and Exchange Commission declined to comment.
"It puts into perspective our increasing dependence on technology and communications," said Bill Baruch, senior market strategist at iiTRADER.com.
"As we put more and more trust in technology for our communications, it brings us back to reality in the sense that these communications are easily misconstrued, easily hacked, so not only can people put out false information, but they can capitalize on it."
Earlier this year, Bloomberg's professional trading platform started incorporating tweets. On Tuesday, spokeswoman Sabrina Briefel said the fake tweet did appear on the Bloomberg terminal. She said the company was not reconsidering its decision to include tweets.
The AP is the latest media organisation to come under siege from hackers in a spate of high profile incidents over the past several months. The New York Times and the Wall Street Journal said their systems were hacked, prompting the White House and lawmakers to push through legislation that will help better defend against cyber attacks.
Reuters News said in August one of its Twitter accounts was hacked and false tweets were posted, mainly related to the armed struggle in Syria.
(Reporting by Susan Heavey and Alina Selyukh in Washington; Gerry Shih in San Francisco; and Jennifer Saba, Dan Burns, Doris Frankel in New York; Writing by Alina Selyukh; Editing by Christopher Wilson, Bill Trott and Philip Barbara)