High-profile Twitterers including Barack Obama, Stephen Fry and Britney Spears had embarrassing or obscene messages posted under their own name after having their accounts hijacked.

Other Twitter users have had their accounts compromised by phishers – scammers who trick people into revealing their log on details – but yesterday's attacks suggest that there may be a security problem inside the firm, experts said.

The hacker used tools that should only be accessible to Twitter staff to help locked-out members reset their email address were accessed by hackers.

"Whoever hacked into those accounts could have hacked in to anyone's - they just chose to go after the big names," said Graham Cluley, senior technology consultant at Sophos.

"This latest attack is actually much more serious than these people and organisations falling for a simple phishing attack.

Telegraph.co.uk