Turner Broadcasting System, which owns CNN, has been hit by a worm that could have been detected if the company had updated its antivirus software. 

According to Symantec's website, the Rinbot worm opens a back door in affected networks and connects to an IRC server, allowing an attacker to send commands to the server. 

The worm spreads using known vulnerabilities in Windows software, including a flaw in Symantec's antivirus software which the security company has patched.

"Only CNN can know what really happened inside its organisation," Graham Cluley, senior technology consultant at Sophos, told vnunet.com. 

"We do know that Delbot, also known as Rinbot, exploits a vulnerability in Symantec's security software, and it is possible that this was a factor in the media company becoming infected."

Cluley said that as hackers become more financially motivated, and take more advantage of security vulnerabilities in their attempt to infect PCs, firms need to ensure that fixes are rolled out as soon as possible.

"Even though Symantec issued a fix for the flaw in its software last year, some companies experience difficulties keeping up-to-date on patches and rolling them out across all of the computers on their network," he said.

CNN was famously hit by another known security flaw back in 2005, when the Zotob worm infected its systems and the breach was reported live on air.

However, the Rinbot botnet is not thought to be a threat to most users, who will be protected against it by now.

"It is possible that some of the media reports have overinflated the impact of the worm," said Cluley.

"One tabloid thought the story was worthy of headline front page news alongside a story about Charlotte Church's pregnancy!"