A computer hacker in France is believed to have accessed control to Twitter's internal computer systems, gaining access to millions of accounts - including US President Barack Obama's.
The hacker, known as "Hacker Croll", put a number of screenshots on the internet which depicted him gaining access to the accounts, and all of the private details buried within them.
The hacker also showed the secret details of President Obama's Twitter account, including the IP address of the person to last update the account.
But Twitter co-founder Biz Stone said that no information was altered or removed, and that the details of only 10 accounts were viewed. He also said that the site is now undergoing an independent security audit.
This is the second time in just four months that the site has been hacked, after an incident in January where a hacker guessed the password to a staff account.
