French police have released a hacker who gained access to US President Barack Obama's account in one of his attacks on the wildly popular micro-blogging site Twitter, police said Wednesday.

The unemployed 25-year-old, who lived with his parents and used the pseudonym "Hacker Croll", was arrested Tuesday after an operation conducted jointly with US agents from the FBI that lasted several months.

He was questioned in police custody in the central city of Clermont-Ferrand and has been ordered to appear in court in the same city on June 24.

"He explained how he did it. He's not a genius," said the source.

"He was a young man spending time on the Internet. He acted as a result of a bet, out of the defiance of the hacker. He is the sort who likes to claim responsibility for what he has done," added prosecutor Jean-Yves Coquillat.

Hacking into a database is a crime in France which carries a maximum two-year prison sentence.

The hacker, who attacked the Twitter accounts of several US celebrities, had also attacked Facebook pages and email accounts operated by Google and other providers, the police said.

But he had never attempted to profit financially from his hacking activities on Twitter, in which users can send out messages of 140 characters or less, they added.

He had managed to secure Twitter's administrator codes and was able to create, modify or delete accounts at will, the source said, adding that the hacker set up a blog to share his discoveries.

The hacker had no particular technological expertise, said police, but simply guessed people's passwords by working them out from information on their blogs or online pages they had created about themselves, police said.

He would also do this by answering the "secret question" on web-based email accounts -- which people often answer by giving their maiden name or the name of their pet -- and then use this to gain access to Twitter passwords.

"Hacker Croll" liked to post electronic copies of the pages he hacked into on French online forums to prove that he gained administrator access to Twitter accounts, according to online reports on his activities.

The French hacker was known to police for minor scams that had netted 15,000 euros (20,000 dollars), according to the police.

The FBI (Federal Bureau of Investigation) alerted French authorities to his presence on French territory in July last year.

Four FBI agents worked with French police for several months to track down "Hacker Croll" and stop the attacks on Twitter, which has millions of users across the world.

In January last year, dozens of Twitter accounts, including that of pop star Britney Spears, were hacked into and fake messages sent out.

Hackers knocked the site offline for several hours last August.

While an everyday chatting tool for many, Twitter has become a weapon used by dissidents to circumvent censorship in places where freedom of speech is suppressed.

Twitter said last month that users were creating 50 million messages per day.

The San Francisco-based Twitter does not release figures on the total number of users of the service, which was launched in August 2006.

- AFP