Bogus terror tweet sparks shares blip US markets suffered a brief but sharp sell-off after a news agency's hacked Twitter account claimed there had been a terrorist attack on the White House. The bogus tweet from Associated Press's main account told its millions of followers that President Barack Obama had been injured in an explosion. The incident underlined the growing influence of Twitter on investor sentiment and the risks associated with inaccurate information being distributed via social media channels. It comes weeks after the US stock market regulator gave companies permission to use social media to communicate with investors. AP's Twitter account, which has 1.9m followers and carries the site's "verified" stamp of authenticity, posted at 1.07pm Eastern Time: "Breaking: Two Explosions in the White House and Barack Obama is injured." Within minutes, @AP's account was suspended while other accounts associated with the news agency, such as AP reporter Sam Hananel, notified their followers that the inaccurate report was the result of a hacking attack. The Federal Bureau of Investigation is investigating the incident. The US Secret Service said its agents were aware of the incident and "will monitor and conduct appropriate follow up." The momentary alarm triggered an 0.9 per cent decline in the S&P 500, wiping more than $130bn off the value of stocks. The index recovered all its losses within minutes. "After the tweet went out, we noticed there was a liquidity gap in the market, where all the buy orders that were out there all of a sudden seemed to be getting cancelled," said Reginald Browne, an executive at Knight Capital. When the tweet seemed to be bogus, the market recovered. He said traders had discussed after the incident how the Securities and Exchange Commission might react in future amid the growing use of social media as a source of official information. Two of the SEC's five commissioners said the agency would look into the bogus tweet. A group calling itself the "Syrian Electronic Army," which has targeted several other Twitter accounts in recent days, claimed responsibility for the hijacking. Social media sites such as Twitter and Reddit faced criticism from some quarters last week, including the White House, after they played host to rumours and speculation about the hunt for the Boston marathon bombing suspects. "In this age of instant reporting, tweets and blogs, there's a temptation to latch on to any bit of information, sometimes to jump to conclusions," Mr Obama said last week. But when a tragedy like this happens, with public safety at risk and the stakes so high, it's important we do this right. Mainstream media outlets such as the New York Post and CNN also played a role in amplifying the online speculation in their traditional newspaper and broadcast formats. AP's is just the latest in a series of Twitter hijackings, adding to pressure on the social media company to improve its security measures. Hackers claiming to be sympathisers of the Syrian government this week took control of accounts belonging to the BBC, Al Jazeera, World Cup football organisers Fifa and broadcaster CBS's @60Minutes show. Brands including Burger King and Jeep have also been affected in recent weeks. Some observers have suggested that such security vulnerabilities could scare advertisers away from Twitter. Tech companies such as Apple and Microsoft have recently introduced two-factor authentication to provide extra protection to their customers.