A British teenager suspected of masterminding a global computer hacking plot from his bedroom could face a fight against extradition to the US.
Ryan Cleary was arrested at his detached family home in Essex today as part of a Scotland Yard and FBI probe into LulzSec, a group claiming responsibility for hacking attempts on the UK's Serious Organised Crime Agency, the US Senate and the CIA.
Neighbours who witnessed the dawn police swoop spoke of their shock as the "very bright" 19-year-old university student was questioned.
Detectives believe Cleary was a "major player" with LulzSec, which has also claimed security breaches at games firms Nintendo and Sony.
As American authorities were kept closely informed over the "pre-planned intelligence-led operation", lawyers said US prosecutors may demand he faces justice across the Atlantic.
Mark Spragg, an extradition lawyer at London-based firm Keystone Law, said: "If the charges on which he was arrested would result in a sentence in excess of 12 months, then potentially it would constitute an extradition offence."
LulzSec is said to have established itself as a formidable splinter group to Anonymous, the hacking group embroiled in the WikiLeaks fallout.
The group was believed to have initially targeted only US 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.
Neighbours of Cleary's family bungalow in Wickford, described him as a "well presented young man".
Dorothy Rounce said she was woken by banging from police officers arresting Cleary in the early hours of this morning.
Her husband, James Rounce, added: "They moved in about 10 years ago and have been pleasant neighbours.
"I think he had been away at university and had come back for the holidays or because he had finished his exams.
"You could tell he was very bright just from the way he spoke and presented himself.
"I knew he was into computers because we would often take in parcels for him and when I asked about them his mother said he was working from home and it was something to do with IT."
Soca, the UK national law enforcement unit dubbed the British FBI, was forced to temporarily 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.
Cleary was arrested by officers from Scotland Yard's specialist e-crime unit. He was being questioned at a central London station under the Computer Misuse Act and Fraud Act.
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, Essex, 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 were working "in co-operation" with the FBI, the spokesman said.
Claims that LulzSec had stolen the entire 2011 UK census database were denied by both the group and security sources.
LulzSec tweeted: "That wasn't us - don't believe fake LulzSec releases unless we put out a tweet first."
And later LulzSec tweeted: "Seems the glorious leader of LulzSec got arrested, it's all over now ... wait ... we're all still here! Which poor bastard did they take down?"
No US arrests have been announced in relation to LulzSec or Anonymous.
LulzSec has been known for several weeks to have been a subject of concern among US authorities.
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.
The FBI is placing "a lot of emphasis and focus on Anonymous and other groups that would be like them, through co-ordinated 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.
The arrest of a Briton in relation to hacking attempts in the US will prompt comparisons with Gary McKinnon.
McKinnon, 45, who is wanted in the US, 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".