LulzSec, the hacking collective loosely associated with Anonymous, suffered a major blow today after law enforcement officials in the U.S. and U.K. arrested three of its members and charged another two with the help of none other than the group's former leader, Hector Xavier Monsegur, better known as "Sabu." Apparently, Monsegur had been secretly arrested months ago and turned into a cooperating witness by the FBI.

The 28-year-old unemployed computer programmer, welfare recipient and legal guardian of two young children allegedly acted as the leader of LulzSec from his apartment in a public housing project in New York. The group famously hacked the security firm HBGary last year before breaking off from Anonymous and going on a high-profile hacking spree targeting Sony, the CIA, the U.S. Senate, and FBI, among many others.

Hector Xavier Monsegur, aka Sabu, LulzSec leading hacker turned FBI informant

In March of 2011, a rival hacker group tired of "the mob's unpatriotic ways", handed law enforcement and a few media outlets a comprehensive list of names and handles associated with Anonymous and LulzSec. Three months later LulzSec announced that it was leaving the hacking world, just as suddenly as it arrived.

Knowing he'd been outed, law enforcement feared Sabu would begin destroying evidence of his hacking career and traces of those he'd worked with online. According to Fox News, they knocked on his door weeks later and after using the clichéd good cop/bad cop routine on him, threatening to take his kids away, Sabu finally gave in. On August 15 he pleaded guilty to a dozen hacking-related charges and agreed to cooperate with the FBI.

As members of LulzSec were arrested over the next months, many hackers had suspected that Sabu was working as a government informant. Indeed, he worked almost daily out of FBI offices, helping the feds identify high-level members of LulzSec and Anonymous. He vehemently denied the accusations, however, and continued to rally the movement on Twitter telling hackers to "Fight back. Stay strong."

Those arrested on Tuesday include Ryan Ackroyd (aka "Kayla") and Jake Davis (aka "Topiary") from London, Darren Martyn (aka "pwnsauce") and Donncha O’Cearrbhail (aka "palladium") from Ireland, and Jeremy Hammond (aka "Anarchaos") from Chicago.

"This is devastating to the organization," said an FBI official involved with the investigation. "We're chopping off the head of LulzSec."