A fake tweet from the Associated Press’ Twitter account that was sent shortly after 1 p.m. EDT on Tuesday indicated that explosions at the White House had injured President Barack Obama, providing yet another example of the dangers inherent in instantaneous social media communications.

The AP Twitter feed was hacked, reportedly by a group called the Syrian Electronic Army, which has compromised the accounts of various other media organizations in the past, including the BBC.

For a few minutes, when people did not realize that the report was a fake, the Dow Jones Industrial Average actually plunged almost 1 percent due to sudden selling by panicked investors -- until sanity prevailed and the AP Twitter account was suspended.

But this has happened before.

On Sept. 9, 2011, just two days before the 10th anniversary of the 9-11 terror attacks, NBC News’ Twitter feed stated: “Breaking news: Ground Zero has just been attacked. Flight 5736 has crashed into the site, suspected hijacking. More as the story develops.”

The next tweet suggested that a second plane might have hit Ground Zero: “Flight 4782 is not responding. One plane just hit Ground Zero site at 5:47. #groundzeroattacked. This is not a joke, Ground Zero has just been attacked. We’re attempting to get reporters on the scene.”

The false story went out to almost 130,000 followers.

Wishing to avoid another panic at such a sensitive time, NBC quickly moved to dispel the report, saying its account was hacked.

Later, NBC stated: “Again -- just a hoax. A really crappy and unfunny hoax. NBC Digital Exec has just confirmed via Twitter: “Ignore tweets from @nbcnews till further notice. We’ve been hacked. Do not retweet.”

A bit later, the network added: “The NBC News twitter account was hacked late this afternoon and as a result, false reports of a plane attack on ground zero were sent to @NBCNews followers. We are working with Twitter to correct the situation and sincerely apologize for the scare that could have been caused by such a reckless and irresponsible act.”

A group calling itself “The Script Kiddies” claimed responsibility for that hack -- and its Twitter account was suspended immediately after the incident.