Ryan Cleary, 24, and Jake "Topiary" Davis, 19, have both entered guilty pleas to two charges of disabling websites belonging to, among others, the National Health Service, News International, Sony, Nintendo, and the Arizona State Police.

Both, however, denied two charges that they had posted "unlawfully obtained confidential computer data" to sites such as the Pirate Bay and Pastebin in a bid to encourage or assist actions contrary to the Serious Crimes Act 2007.

Cleary additionally pleaded guilty to four further hacking charges, including attacks on US Air Force computers at the Pentagon, and denied four charges under the Computer Misuse Act 1990.

The four charges made against Davis were also made against Ryan "Kayla" Ackroyd, 26, and a 17-year-old who cannot be named for legal reasons. Both Ackroyd and the 17-year-old entered pleas of not guilty.

All four men were appearing at Southwark Crown Court in London.

Cleary and Davis were both members of Lulz Security, or "LulzSec," which ran a 50-day hacking campaign in 2011. The group, broadly affiliated with Anonymous, hacked some servers, took others offline with distributed denial-of-service attacks, and published large quantities of personal information including usernames, passwords, and e-mails.

Ryan Cleary was arrested for his participation in June 2011. Shortly after, Jake Davis was also arrested.

After his arrest, Cleary was originally released on bail, but was later jailed after contacting LulzSec leader Hector "Sabu" Monsegur in breach of his bail conditions: it was revealed in March this year that Monsegur had been arrested in early June 2011, and then worked secretly as an FBI informant.

Cleary has also been indicted in the US for attacks on Sony, PBS, and Fox. Extradition to the US to face these charges is, however, unlikely, with US prosecutors saying that he should be dealt with in the UK's courts.

Ackroyd, Davis, and the 17-year-old have been released on bail, with Cleary remaining in custody. Ackroyd and the 17-year-old are due to stand trial in April, 2013 for all four charges. The Crown Prosecution Service is still considering whether to take Davis and Cleary to trial for the two charges they denied.