An unknown party has hacked into the Twitter accounts of high-profile users of the micro-blogging and social networking service such as US President-Elect Barack Obama, Britney Spears, and Fox News anchor Bill O'Riley.

(Credit: Twitter, screenshot by Ian Schafer)

The hacker posted embarrassing messages on their victims' accounts; for example, CNN anchor Rick Sanchez' site said he was "high on crack" and "might not be coming into work today".

"This morning we discovered 33 Twitter accounts had been 'hacked', including prominent Twitterers like Rick Sanchez and Barack Obama," US-based Twitter confirmed in a statement on its company blog. "We immediately locked down the accounts and investigated the issue.

"Rick, Barack and others are now back in control of their accounts."

Twitter said the hacking issue was different from a phishing scam which had been targeting Twitter users over the weekend, with the accounts being compromised by a hacker who broke into some of the tools used by its support team.

"We considered this a very serious breach of security and immediately took the support tools offline," the start-up wrote. "We'll put them back only when they're safe and secure."

Twitter noted it was planning to start beta testing a new security authentication protocol called OAuth soon; however, the start-up wrote that this would not have prevented either problems.