NEW YORK: One of the world's most-wanted hackers secretly became an FBI informant last year, providing evidence that led to charges on Tuesday against five other suspected leaders of the Anonymous international hacking group.

In a major blow to Anonymous, which has attacked the websites of government agencies and companies around the world, US authorities revealed that a leading hacker “Sabu” was Hector Xavier Monsegur and that he was arrested at his small apartment in a Manhattan housing complex last June.

At a secret court hearing on August 15, 2011, Monsegur, 28, pleaded guilty to each of the 12 computer crimes and agreed to cooperate with authorities in exchange for leniency, according to a transcript that was made public on Tuesday.

US prosecutors and the FBI on Tuesday announced charges against five other men, including two in Britain and two in Ireland who were all previously arrested.

The fifth was Jeremy Hammond, known as “Anarchaos,” who was arrested in Chicago on Monday on charges of hacking into Strategic Forecasting Inc, or “Stratfor”, a global intelligence and research firm, in December 2011. All six were top members of LulzSec, an offshoot of the loose-knit international cyber-activist group Anonymous.

“These cyber criminals affiliated themselves with Anonymous in different ways. They are not Anonymous today, they have been identified and charged,” said a law enforcement official, who did not want to be identified as the investigation was ongoing.

LulzSec and Anonymous have taken credit for carrying out attacks against the CIA, Britain's Serious Organized Crime Agency, Japan's Sony Corp, Mexican government websites and the national police in Ireland. Other victims included Rupert Murdoch's UK newspaper arm News International, Fox Broadcasting and Sony Pictures Entertainment.

Cyber security experts said the arrests were a major setback for Anonymous and other hacking groups affiliated with it. “Sabu was seen as a leader ... Now that Anonymous realizes he was a snitch and was working on his own for the Fed, they must be thinking: 'If we can't trust Sabu, who can we trust?'” said Mikko Hypponen, chief research officer at Finnish computer security company F-Secure.

“It's probably not going to be the end of Anonymous, but it's going to take a while for them to recover, especially from the paranoia,” Hypponen said.

Other experts said it remained to be seen if the arrests would put an end to illegal hacking by Anonymous affiliates.