Authorities in the U.S., Britain, and Ireland have brought charges against five hackers from the hackers group LulzSec, which is allegedly responsible for a raft of computer attacks that have robbed personal data from more than a million people and cost companies billions of dollars. And in a remarkable twist, the group was brought down by its own leader, known in the hacking world as "Sabu." (After being arrested last June, Sabu agreed to cooperate with the FBI.) "This is devastating to the organization," an FBI official tells Fox News. "We're chopping off the head of LulzSec." Here's what you should know about this "stunning" case:

What exactly is LulzSec?
The group — known more formally as Lulz Security — is an offshoot of the global hacking collective Anonymous. The groups are intertwined, with overlapping membership. They have no clear ideological agenda, though they support various causes that seek to undermine state institutions and big businesses. Both groups, for example, are strong allies of WikiLeaks. LulzSec has an impish streak ("lulz" is internet slang for laughs), with a reputation for making trouble for the sheer anarchic pleasure of it. 

What is LulzSec accused of doing?
LulzSec and Anonymous have allegedly hacked the computer systems of numerous companies, institutions, and governments. Alleged corporate targets include Fox News, Sony, PBS, Visa, Mastercard, and PayPal. The hackers have also allegedly attacked the FBI and the U.S. Senate, as well as federal contractors with sensitive cybersecurity information. The governments of Zimbabwe, Yemen, Algeria, and Tunisia have also been apparent victims. In December, the hackers allegedly breached the intelligence firm Stratfor, unlocking the names, email addresses, and credit-card information of its clients. In February, WikiLeaks released emails taken from the Stratfor hack. 

How did the FBI uncover the hackers' identities?
First, an anonymous tipster gave Sabu away, according to The Wall Street Journal. Sabu then pleaded guilty to 12 counts of hacking, for which he faces 124 years in prison. Sabu — who is actually 28-year-old Hector Xavier Monsegur, a single father of two who lives in New York City — reportedly chose to inform on his comrades in exchange for a lighter sentence. While he was cooperating with the feds, Sabu continued to appear on hacker message boards, encouraging them to keep up the anti-establishment fight. His last tweet, quoting the communist martyr Rosa Luxembourg, read, "The revolution says I am, I was, I will be."

Who is charged in the crackdown?
In addition to Sabu, authorities brought charges against two men in Britain, two men in Ireland, and one man in Chicago. Previously known only by pseudonyms — such as "pwnsauce" and "Anarchaos" — the five men are accused of multiple crimes, and face as many as 10 years in prison for each charge. One man, Jeremy Hammond of Chicago, is thought to be the leader behind the Stratfor attack.

What does this mean for hackers?
"This is a stunning development," says Adrian Chen at Gawker. Sabu was the most "prominent and revered" member of the group, and acted as its "de facto spokesman." Sabu's downfall and deception "will sow even more distrust and dissension in the ranks of Anonymous," says Somini Sengupta at The New York Times. Hackers won't just be on the lookout for the feds — they'll be eyeing each other with suspicion, too. 

Sources: Fox News, GawkerThe New York Times, PCWorldTalking Points Memo, The Wall Street Journal