Cleary confessed to launching a string of cyber-attacks on major institutions in Britain and the US with fellow hacker Jake Davis (19). The duo targeted various sites including the NHS, News International, Sony, Nintendo, Arizona State Police, and film studio 20th Century Fox in a series of so-called distributed denial of service (DDoS) attacks, where websites are flooded with traffic to make them crash.
Cleary and Davis plotted to carry out the attacks with other unknown members of internet groups Anonymous, Internet Feds, and LulzSec.
Cleary also confessed today to four separate charges, including hacking into US Air Force Agency computers, based at the Pentagon.
Both men appeared in the dock at Southwark Crown Court, London, to enter guilty pleas to a series of charges brought against them. But both accused denied allegations they posted "unlawfully obtained confidential computer data" to public websites including LulzSec.com, Pirate Bay, and PasteBin, in order to encourage offences contrary to the Serious Crime Act.
Alleged co-hackers Ryan Ackroyd (25) and a 17-year-old A-level student, from south-London, deny their involvement in the DDoS attacks and will stand trial on April 8, 2013.
'LulzSec' is a combination of 'lulz' , meaning 'laugh out loud' and security.
Davis, of Lerwick, Shetland; and Cleary, of Wickford, Essex, pleaded guilty to two counts of conspiracy to do an unauthorised act or acts with intent to impair, or with recklessness as to impairing, the operation of a computer or computers.
All the accused, apart from Cleary, were released on bail.