Image caption The Lulz Security group has used Twitter to draw further attention to itself

A hacker group that has attacked several high-profile websites over the last two months has announced that it is disbanding.

Lulz Security made its announcement through its Twitter account, giving no reason for its decision.

A statement published on a file-sharing website said that its "planned 50-day cruise has expired".

The group leapt to prominence by carrying out attacks on companies such as Sony and Nintendo.

Broadcasters Fox and PBS, the CIA, and the United States Senate have also been cyber-attacked by the group.

As a parting shot, the group released a selection of documents apparently including confidential material taken from the Arizona police department and US telecoms giant AT&T.

Correspondents say LulzSec's announcement could be a sign that its members are nervous because of recent police investigations, including the arrest of a British man suspected of links to the group, and efforts by rival hackers to expose them.

'Microscopic impact'

Analysis The disbanding of LulzSec might seem like an important victory for the forces of law and order - after all, this is the group credited with attacks on everything from Sony to the CIA. But in this shadowy world of claims, boasts and posturing, nothing is quite what it seems. It may have been other members of the hacker "community" - disgruntled with the antics of LulzSec - who forced the group into retreat. A document posted online in the last 24 hours purports to be a history of LulzSec, complete with full details on its leaders. "We've been tracking and infiltrating these kids," says the document, and its account goes on to name people in the UK, Amsterdam and New York, along with their social networking profiles and other details. The document, posted by something called the A-Team, looks convincing, with logs from IRC (Internet Relay Chat) conversations amongst the group. It ends by offering the "raw logs of everything" to any law enforcement agency. But even if LulzSec has gone offline, its members and other hackers trying to make a name for themselves may soon pop up elsewhere. And the other question is whether we should take any publicity-hungry group like this too seriously. The real damage is more likely being done by criminal groups who wouldn't dream of boasting of their exploits on Twitter or anywhere else.

The group's identities remain anonymous and it has not been possible to contact its members directly to confirm its statement.

The statement said that "our crew of six wishes you a happy 2011".

"So with those last thoughts, it's time to say bon voyage," it added.

"Our planned 50 day cruise has expired, and we must now sail into the distance, leaving behind - we hope - inspiration, fear, denial, happiness, approval, disapproval, mockery, embarrassment, thoughtfulness, jealousy, hate, even love. If anything, we hope we had a microscopic impact on someone, somewhere."

But LulzSec urged its supporters to carry on.

"We hope, wish, even beg, that the movement manifests itself into a revolution that can continue on without us," the statement said.

"Please don't stop. Together, united, we can stomp down our common oppressors and imbue ourselves with the power and freedom we deserve."

The group had previously told the BBC's Newsnight programme that it wanted to target the "higher ups" who write the rules and "bring them down a few notches".

In an online Q&A, the hacker known as Whirlpool, who described himself as "captain of the Lulz Boat", said that while the group had begun hacking "for laughs" - for which the word "lulz" is cyber-slang - it evolved into "politically motivated ethical hacking".

And in an interview with the Associated Press on Friday, a LulzSec member said the group had at least five gigabytes of "government and law enforcement data" from around the world, which it planned to release in the next three weeks.

Ryan Cleary, 19, from Wickford, Essex, was arrested as part of a Scotland Yard and FBI probe into LulzSec and charged with hacking the website of the UK Serious Organised Crime Agency.