LulzSec hackers have admitted they were behind cyber attacks against the CIA, the NHS and the Serious Organised Crime Agency.
Ryan Cleary, 20, and Jake Davis, 19, pleaded guilty yesterday at Southwark Crown Court, south London, to charges that they carried out distributed denial of service (DDoS) attacks on the institutions' websites last year, a court official said.
Other victims of the pair included News International, Arizona State Police, Nintendo, Sony and 20th Century Fox.
But Cleary, from Wickford, Essex, and Davis, from Lerwick, Shetland, denied "posting unlawfully obtained confidential computer data to public websites" such as LulzSec.com.
Alleged accomplices Ryan Ackroyd, 25, from Mexborough, South Yorkshire, and a 17-year-old from south London, who cannot be named for legal reasons, deny carrying out the DDoS attacks and posting unlawfully obtained material online. They will stand trial on April 8 next year.
Cleary, who has been diagnosed with Asperger's syndrome, also admitted four separate charges including an attack on Pentagon computers.
Cleary and Davis admitted yesterday they plotted the attacks with other unidentified hackers belonging to online groups such as LulzSec, Anonymous and Internet Feds.
The DDoS attacks they carried out flood websites with traffic, making them crash and rendering them unavailable to users.
To achieve this, they used a remotely controlled network of "zombie" computers, known as a "botnet", capable of being programmed to perform the attacks.
On June 15 it emerged that American authorities are not expected to seek Cleary's extradition to the US, where he is subject to an indictment for the same charges he was answering in London today.
LulzSec was formed last May as a spin-off of the loosely organised hacking collective Anonymous.
Lulz is internet slang that can be interpreted as "laughs", "humour" or "amusement", and Sec refers to "security".