NEW YORK (CNN) -- Top members of the computer hacker group "Anonymous" and its offshoots were arrested and charged Tuesday after a wide-ranging investigation used the help of a group leader who was working as a secret government informant.
Five of the suspects, considered by investigators among the "most sophisticated hackers in the world," were arrested in the United States and Europe and charged in a Manhattan federal court over their alleged role in high-profile cyberattacks against government agencies and large companies, according to an indictment.
A sixth man, Hector Xavier Monsegur, a notorious hacker known as "Sabu," pleaded guilty in August to computer hacking and other crimes.
As part of his plea deal, Monsegur cooperated with government investigators and helped build a case against the five other defendants, according to a source with knowledge of the investigation.
Ryan Ackroyd, 23; Jake Davis, 29; Darren Martyn, 25; and Donncha O'Cearrbhail, 19, have been charged with conspiracy regarding attacks against Fox Broadcasting Co., Sony Pictures Entertainment and the Public Broadcasting Service, or PBS.
O'Cearrbhail is also accused of hacking into the personal e-mail account of an Irish national police officer and eavesdropping on a conference call between Irish police, the FBI and other law enforcement agencies about ongoing investigations into Anonymous and other hacker groups. The suspect allegedly recorded the call and disseminated the recording to other hackers.
Jeremy Hammond, 27, was charged with a December cyberattack against a Texas firm called Strategic Forecasting Inc., which authorities say might have affected about 860,000 people.
O'Cearrbhail and Martyn are from Ireland, and Hammond is from Chicago, the indictment said.
Ackroyd and Davis are from Britain.
Monsegur, 28, in August pleaded guilty to 12 counts of computer hacking and other crimes.
Known as a "rooter," the New York City resident identified vulnerabilities in a variety of computer systems and then passed along that information to other hackers.
Monsegur and others have claimed responsibility for cyberstrikes between December 2010 and June 2011 that included denial of service attacks against the websites of Visa, MasterCard and PayPal.
A denial of service (DoS) attack typically involves the use of a large number of computers to bombard websites with phony requests for information, causing the site to temporarily shut down.
Dubbed "Operation Payback," authorities say the credit card and PayPal attacks were prompted by the firms' refusals to process donations to WikiLeaks, an organization that facilitates the anonymous leaking of secret information. The group's website has released thousands of classified diplomatic cables as well as confidential -- and, at times, controversial -- messages about the wars in Iraq and Afghanistan.
Authorities say Monsegur also hacked or launched DoS attacks against computer systems operated by the governments of Tunisia, Yemen, Algeria and Zimbabwe.
Beginning in December 2010, the indictment said, Monsegur, Ackroyd, Davis, Martyn and O'Cearrbhail conspired as a splinter hacker group called Internet Feds and penetrated the website of Fine Gael, an Irish political party, as well as the computer systems of a security firm called HBGary Inc. and its affiliates.
The group allegedly stole confidential data from about 80,000 user accounts associated with the firm.
Then in 2011, apparently feeling the heat from investigators, the group formed another offshoot organization called Lulz Security, or LulzSec, the indictment said.
LulzSec then ratcheted up "a campaign of malicious cyberassaults on the websites and computer systems of various business and governmental entities in the United States and throughout the world."
Barrett Brown, who identifies as an Anonymous spokesman, told CNN that Sabu recently took over leadership of LulzSec.
He said the hacker also contacted him several months ago by instant message, and he described those communications as "weird."
"There have always been rumors from a couple of people (within Anonymous) something weird was going on with LulzSec when (Sabu) started," said Brown, whose Dallas apartment was visited by FBI agents early Tuesday morning.
Brown said that he and others in Anonymous were upset with LulzSec and Sabu because Sabu had bragged about stealing credit card information.
Still, he says, Tuesday's indictments won't disrupt the organization's actions over the long-term.
"There are more than enough people around," he said. "Major operations going forward won't be interrupted.
Authorities have said that leader within the organization was secretly working with government officials and aided their investigation.
Anonymous is considered a loosely tied group of hackers, that have spawned affiliate bodies, and in recent years have focused their efforts on coordinating cyberattacks for political reasons or as retribution for the activities of governments and large corporations.
CNN's Ashley Fantz and Viviene Foley contributed to this report