Two British members of the notorious Lulz Security hacking collective pleaded guilty to a slew of computer crimes Monday, the latest blow against online troublemakers whose exploits have grabbed headlines and embarrassed governments around the world.

Ryan Cleary, 20, and Jake Davis, 19, pleaded guilty to conspiring with other members of LulzSec to attack government, media, and law enforcement websites last year, according to Gryff Waldron, an official at London's Southwark Crown Court.

LulzSec -- an offshoot of the loose-knit computer hacking collective known as Anonymous -- has claimed responsibility for attacks against sites run by the Central Intelligence Agency, the U.S. Public Broadcasting Service, and Rupert Murdoch's News International. Other targets included media and gaming companies such as Nintendo and Sony, tech security company HBGary, Britain's National Health Service, and Arizona State Police.

Waldron said that two other defendants -- Ryan Ackroyd and an unnamed teenager -- have pleaded not guilty to the same charges. All four have denied encouraging or assisting others to commit fraud or other computer offenses.

Cleary, one of the first LulzSec conspirators to be arrested, also pleaded guilty to providing the hackers with illegally-hijacked computer networks for use in denial-of-service attacks, which overwhelm websites by flooding them with bogus traffic. He has also admitted breaching the Pentagon's cyberdefenses by installing or altering files on U.S. Air Force Agency computers.

Cleary faces a U.S. federal indictment in relation to his cyberattacks, but his attorney has said she would "fiercely contest" any moves to extradite her client to America.