A 19-year-old man is suspected of leading the notorious Lulz Security hacking group

A British teenager suspected of being a mastermind behind a notorious international computer hacking group has been arrested in a swoop by the FBI and Scotland Yard.

Ryan Cleary, 19, is believed to have been a 'major player' with LulzSec, a hacking group linked with attempts to breach organizations including the UK's Serious Organized Crime Agency, the U.S. Senate and the CIA.

The arrest came amid claims on the website Pastebin that LulzSec allegedly had a copy of Britain's entire census database and was planning to publish it online, but this has been denied by the Office of National Statistics and by LulzSec via Twitter.

Authorities on both sides of the Atlantic have been trying to trace the hacking group, which also claimed credit for security breaches at games firms Nintendo and Sony, for several weeks.

Cleary was arrested in a 'pre-planned intelligence-led operation' in Wickford, Essex, the Metropolitan Police said.

American authorities were being kept informed as the teenager was questioned at a central London station under the Computer Misuse Act and Fraud Act.

He was arrested by officers from the force's e-crime unit.

LulzSec is said to have established itself as a formidable splinter group to Anonymous, the hacking group embroiled in the WikiLeaks fall-out.

The group was believed to have initially targeted only U.S. broadcasters, including PBS and Fox, and gaming firms.

But the Twitter page @LulzSec recently declared its intention to break into Government websites and leak confidential documents.

There were no tweets in reaction to the arrest today.

Soca, the UK national law enforcement unit dubbed the British FBI, was forced temporarily to take its website off-line yesterday after LulzSec bombarded it with traffic to stop other users accessing it.

Security sources were keen to underline that no confidential information was surrendered.

A Scotland Yard spokesman said: 'The arrest follows an investigation into network intrusions and distributed denial of service attacks against a number of international business and intelligence agencies by what is believed to be the same hacking group.

'Searches at a residential address in Wickford following the arrest last night have led to the examination of a significant amount of material. These forensic examinations remain ongoing.'

The Met and Essex Police are working 'in co-operation' with the FBI, the spokesman said.

Soca spokesman Richard Sellors said: 'We are aware of claims that the Soca website has been attacked. The picture is not clear at this time, but we are investigating the matter with our service provider.'

The website went down for a while yesterday afternoon but it was brought back up.

Mr Sellors said Soca then decided to take the site down for the night to take the pressure off its Internet service provider, which works with a variety of local businesses and organizations.

The website was still down this morning.

Mr Sellors said that the affected website was purely for public information and that the hackers had no access to confidential data or information about ongoing operations.

LulzSec has also hacked into a U.S. Senate server and claimed responsibility for temporarily knocking offline the CIA's public website.

In a posting on Sunday, LulzSec declared that the 'Lulz Lizard battle fleet is now declaring immediate and unremitting war' on governments and security companies.

As part of that, LulzSec, which derives its name from the plural variant of internet slang for 'laugh out loud', urged its followers to hack into and deface government websites.

TIMELINE OF RECENT HIGH- PROFILE CYBER ATTACKS

April 29: Fox Broadcasting alerted its users that it had been hacked, and attackers gained access to emails and passwords of hundreds of employees

May 29: PBS website hacked; user names and hashed passwords released. A false story was also posted claiming rapper Tupac Shakur was 'still alive in New Zealand' 15 years after his death

June 2: SonyPictures.com hacked and personal information of its one million users compromised

June 5: Nintendo announces its computer system was hacked, but no personal or company information was lost

June 8: NHS confirms potential security breach after computer hackers gained access to health service passwords

June 10: IMF confirms it was hit over several months by what it called 'a very major breach'

June 13: Lulz Security accessed a Senate server that supports the chamber's public website but did not breach other files

June 16: LulzSec claims cyber attack on CIA computer network, causing public website to shut down

June 20: LulzSec brings down the Serious Organised Crime Agency's website

Lulz said in the statement on Sunday: 'Top priority is to steal and leak any classified government information, including email spools and documentation. Prime targets are banks and other high-ranking establishments.'

LulzSec said it was working with Anonymous, a second international group of hackers.

The groups' stated goals have been murky.

In the past, Anonymous has sought to support Julian Assange and Bradley Manning, who face charges after releasing U.S. government documents as part of Wikileaks.

LulzSec has also sought to punish Sony for failing to secure data but did so by releasing the data of Sony customers, exposing them to potential identity theft.

Meanwhile, a less public and more damaging series of hacks have targeted the International Monetary Fund and RSA, a division of EMC, a company which provides online security for businesses.

Steven Chabinsky, the FBI's deputy assistant director, told the Financial Times last week that LulzSec and Anonymous were avoiding prosecution by using the likes of Twitter to draw supporters under an anonymous guise.

Mr Chabinsky told the paper: 'These organizations have managed to use new technologies to connect to otherwise disenfranchised hackers to gather force and momentum in a way we have not seen before.'

The FBI is placing 'a lot of emphasis and focus on Anonymous and other groups that would be like them, through coordinated transnational efforts', he added.

Anonymous came to prominence last year when it launched digital assaults against MasterCard, PayPal and other businesses that stopped working with WikiLeaks.

No U.S. arrests have been announced in relation to LulzSec or Anonymous.

The arrest of a Briton in relation to hacking attempts in the U.S. will prompt comparisons with Gary McKinnon.

McKinnon, 45, who is fighting extradition to the U.S., faces 60 years behind bars for hacking into Pentagon and NASA computers between February 2001 and March 2002 while searching for evidence of 'little green men'.