False tweet that Obama was injured raises social media doubts

When a false report of explosions at the White House instantly wiped more than US$136 billion off the value of US stocks, Jonathan Corpina did not need a powerful computer.

He used the tool favoured by traders for more than a century: a phone. Corpina, senior managing partner with Meridian Equity Partners, who works on the floor of the New York Stock Exchange, called a client two blocks from the US president's house.

"He did not know what I was talking about," Corpina said. "He said 'I'm staring at the White House and there's nothing going on here right now'."

Less than a month after social media received US regulators' blessing to be a source for market-moving news, the hacking of the Associated Press' Twitter account is raising concerns over the trustworthiness of information spread via the site.

Stocks tumbled about 1 per cent on Tuesday after the AP, one of the world's largest news agencies, sent out the fake Twitter post about explosions at the White House, which had supposedly injured President Barack Obama. DJIA stocks, which had dipped 150 points on the report, eventually recovered after AP blamed a hacking attack. It removed the account.

A group called the Syrian Electronic Army claimed responsibility for the attack. The group's Twitter account is linked to the website Syrianelectronicarmy. com, an Arabic language site that broadcasts what the group says are its latest computer attacks.