A teenager has been arrested in a joint Scotland Yard and FBI investigation into the hacking of websites.
The 19-year-old man was held during a raid at a house in Wickford, Essex.
On Monday the UK's Serious Organised Crime Agency (Soca) took its website offline after it was attacked by Lulz Security hackers.
Scotland Yard would not confirm the arrest was connected but did say that it followed a series of distributed denial of service (DDoS) attacks.
The raid in Essex was a "pre-planned, intelligence-led" operation, it said.
The teenager was arrested under the Computer Misuse Act and Fraud Act and is being questioned at a central London police station.
He was arrested by the Metropolitan Police's e-crime unit.
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."
Scotland Yard is co-operating with the FBI as well as Essex Police.
An FBI spokesman said they had no comment "at this time".
When Lulz Security, or LulzSec, first appeared in May, the group portrayed itself as a light-hearted organisation, bent on creating online fun and Lulz (laughs).
But LulzSec is said to have been planning to established itself as a rival to Anonymous, the hacking group embroiled in the WikiLeaks fallout.
LulzSec initially targeted US broadcasters PBS and Fox and gaming firms.
But the Twitter page @LulzSec then declared its intention to break into government websites and leak confidential documents.
Channel 4 News claimed LulzSec may have succeeded in hacking into the database of the 2011 census, which hold details of every UK citizen who filled out the survey earlier this year.
LulzSec is also suspected of hacking into CIA, Sony and NHS websites.
----------------------------
Lulz Security attacks
May 7: US X Factor contestant database
May 10: Fox.com user passwords
May 15: Database listing locations of UK cash machines
May 23: Sonymusic Japan website
May 30: US broadcaster PBS. Staff logon information
June 2: Sonypictures.com user information
June 3: Infragard website (FBI affiliated organisation)
June 3: Nintendo.com
June 10: Pron.com pornographic website
June 13: Senate.gov - website of US Senate
June 13: Bethesda software website. User information
June 14: EVE Online, League of Legends, The Escapist and others
June 20: Soca website taken offline
June 21: National Census database reportedly attacked
http://www.bbc.co.uk/news/technology-13859868