Hector Xavier Monsegur, leader of elite hacking group LulzSec, is one of the most wanted computer vandals in the world and secretly began working as an FBI informant months ago, the FBI revealed upon Tuesday's arrests.
Five LulzSec members were charged in court papers unsealed in federal court in New York. Authorities revealed that the sixth person, Monsegur, pleaded guilty to charges of conspiracy to engage in computer Hacking and other offenses Aug. 15.
Monsegur and his followers embarked on exploits against business and government entities in the U.S. and around the world, resulting in the theft of confidential information, the defacing of websites and attacks that temporarily put victims out of business. Their targets included cyber-security firms.
Meanwhile, Ireland's national police confirmed that detectives had arrested a member being sought by international law enforcement and that he was being held at a south Dublin police station. The person's name has been withheld.
Some alleged LulzSec associates are already facing charges elsewhere. An English teenager, Ryan Cleary, was arrested by British law enforcement in June and charged with being linked to the group. In July, reputed LulzSec spokesman Jake Davis was arrested in Scotland.
LulzSec is short for Lulz Security. The group is a branch of Anonymous, the world's most well-known group of hackers. Anonymous attained notoriety last May by attacking the website of the public broadcaster PBS and posting a story claiming that the slain rapper Tupac Shakur was alive and living in New Zealand.
The Associated Press contributed to this report.