(Reuters) -- Six suspected leaders of the international hacking organization known as Anonymous were charged by U.S. authorities of computer crimes, dealing a major blow to the loose-knit group that has wreaked havoc on the websites of government agencies and major corporations.

Among those charged was Hector Xavier Monsegur, known as Sabu, who took responsibility for attacks on the websites of eBay's PayPal, MasterCard Inc and Visa Inc between December 2010 and June 2011, according to federal prosecutors and the FBI. The attacks were in retaliation for the refusal of those companies to process donations to Wikileaks, the group that leaked confidential diplomatic cables in 2010.

The charges against Monsegur, in a case that was opened last summer, were filed in federal court in New York via a criminal information. Such a document typically means a suspect has been cooperating with the government.

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 Hyponnen, 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, Hyponnen said.

Monsegur pleaded guilty last August to 12 charges, including computer hacking and conspiracy, according to documents unsealed in New York federal court on Tuesday. He is free on a $50,000 bond. The charges carry a possible maximum prison term of 10 years.

Monsegur has also identified himself as a member of hacking groups called Internet Feds and LulzSec, the office of the Manhattan U.S. Attorney and the FBI said in a statement.

U.S. authorities also said they had arrested Jeremy Hammond in Chicago on Monday, on charges of hacking in to Strategic Forecasting Inc, or Stratfor, a global intelligence and research firm, in December 2011. Hammond, who was also known as Anarchaos and other names, identified himself as a member of AntiSec hacking group, authorities said.

In publicizing the Stratfor hack, members of AntiSec reaffirmed their connection to Anonymous and other related groups, including LulzSec, the statement said. It said members published a document with links to Stratfor data entitled: Anonymous Lulzxmas rooting you proud on a file-sharing website.

About 860,000 clients and subscribers of Stratfor had confidential information stolen, officials said.

A lawyer for Monsegur, Peggy Cross, did not immediately return a call seeking comment on the charges. Hammond's lawyer could not immediately be identified.

U.S. authorities said the cyber attacks had affected more than 1 million people and the computer systems of foreign governments, such as Algeria, Yemen and Zimbabwe. Authorities said Monsegur and three of the charged men raided personal information about 70,000 potential contestants on Fox Television show X-Factor.

Anonops, which sends online messages on behalf of Anonymous, sent a message on Twitter following the arrests. #Anonymous Is an idea, not a group. There is no leader, there is no head. It will survive, before, during, and after this time, Anonops tweeted just after noon on Tuesday.

LulzSec, an underground group also known as Lulz Security, along with parent group Anonymous have taken credit for carrying out a number of hacking actions against companies and institutions including the CIA, Britain's Serious Organized Crime Agency, Japan's Sony Corp, Mexican government websites and the national police in Ireland.

A spokesman for Irish police said one of the suspects had been arrested and was being held in Terenure, a middle-class suburb of Dublin.

Last summer, as part of a coordinated law enforcement raid on the group, British police arrested Jake Davis, another suspected member of LulzSec who went by the nickname Topiary.

One of the charges announced on Tuesday was against Davis, a teenager accused of computer attacks on Sony, UK crime and health authorities, and Rupert Murdoch's UK newspaper arm News International.

Davis is believed to have controlled the main Twitter account of Lulz Security, which the group used to publish data obtained by hacking into corporate and government networks.

LulzSec and Anonymous, loose online collectives of activists, have attracted widespread global media coverage for their stunts. LulzSec has more than 350,000 followers on Twitter.

Last month, Anonymous published a recording of a confidential call on January 17 between FBI agents and London detectives in which the law-enforcement agents discuss action they are taking against hacking. Authorities said they had arrested and charged Donncha O'Cearrbhail, 19, of Birr, Ireland of computer hacking conspiracy.

(Reporting By Basil Katz, Grant McCool; Additional Reporting by Diane Bartz, Lorraine Turner, Georgina Prodhan; editing by Mark Porter, Derek Caney and Matthew Lewis)

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