False tweets from major news organisations about a plane crash at New York's Ground Zero and the death of Steve Jobs caused widespread online panic over the weekend and even piqued the interest of the FBI.
The incidents underscore the ease with which false news can spread at lightning speed on the internet. They come after the Fox News Twitter account was hacked to spread a hoax about the death of US President Barack Obama.
The NBC News Twitter feed - which has over 130,000 followers - was hacked by a group that claimed a hijacked plane, in a fresh attack, had crashed into the site where New York's twin towers were destroyed in September 11 attacks 10 years ago.
"Breaking News! Ground Zero has just been attacked. Flight 5736 has crashed into the site, suspected hijacking. more as the story develops," the tweet read.
It was soon followed by: "Flight 4782 is not responding, suspected hijacking. One plane just hit Ground Zero site at 5:47."
A follow-up message sent minutes later said: "This is not a joke. Ground Zero has just been attacked. We're attempting to get reporters on the scene."
The hoax by a group called The Script Kiddies came just before the United States marked the 10th anniversary of the 2001 attacks on New York's World Trade Center and the Pentagon in Washington. The US was already on high alert after receiving intelligence that new attacks were in the works.
In a statement NBC apologised for the scare and said it was working with Twitter to rectify damage caused by the "reckless and irresponsible act".
The NBCNews Twitter account was briefly suspended before reappearing, and the FBI has confirmed its computer crimes unit is investigating the incident.
The hacking group The Script Kiddies appears to be an offshoot of the Anonymous and LulzSec hacking collectives, both of which have been targets of FBI investigations.
The group's goal is to embarrass news outlets and it recently took credit for hacking the Fox News Twitter account to post false information about a fatal shooting of US President Barack Obama.
NBC said its Twitter password was only known by three executives and it suspected the hack may have occurred after an employee clicked on a malicious email attachment.
On the same day NBC's Twitter account was hacked, broadcaster CBS tweeted from its What's Trending account: "Reports say that Steve Jobs has passed away. Stay tuned for more updates."
The tweet sparked a frenzy on the web with tech bloggers rushing to get to the bottom of the rumour. However, CBS later retracted the tweet saying "Apologies- reports of Steve Job's death completely unconfirmed. Live on."
CBS News has now severed its relationship with the organisation responsible for publishing the tweets, according to the Hollywood Reporter.
However, the tech blog Gizmodo believes the Jobs death rumour could have some truth to it. Jobs stepped down from the Apple CEO job last month and has since been photographed looking very ill.
- Sydney Morning Herald