The US Federal Bureau of Investigation (FBI) is probing the hacking of the NBC News Twitter account.
The hackers posted bogus Tweets about the hijacking of a civilian airliner that supposedly crashed into Ground Zero in New York, according to US reports.
The first Tweet said: "Breaking News! Ground Zero has just been attacked. Flight 5736 has crashed into the site, suspected hijacking. More as the story develops."
The Tweets were taken down eight minutes after they appeared on the main NBC News Twitter account on Friday. The Twitter hoax appeared at a time of heightened security in the US in the run up to the 10th anniversary of the 9/11 attacks.
The FBI has confirmed its computer crimes unit is investigating the latest in a series of cyber attacks on government and private companies.
In text pasted into the NBC News Twitter profile, the attackers claimed to be from a group called "The Script Kiddies", an offshoot from hacking groups Anonymous and Lulz Security (LulzSec).
Both hacking groups have been under intensive investigation by the FBI on both sides of the Atlantic in co-operation with UK and other European law enforcement agencies.
Observers say the main goal of "The Script Kiddies" appears to be to embarrass news organisations.
The NBC News Twitter hacking comes just two months after the group took credit for a similar attack on the Fox News Twitter account, in which false information was posted about a fatal shooting of US President Barack Obama.
Ryan Osborn, the NBC director of social media, has admitted clicking recently on an attachment of an e-mail from an unknown sender.
Security experts believe the attachment may have activated a key logger program used to capture Osborn's username and password for the NBC News Twitter account.