LulzSec mastermind "Sabu" was identified today as 28-year-old Hector Monsegur, who has been working with the FBI since being arrested last summer and pleaded guilty to computer hacking crimes. We're digging into court documents and planning detailed coverage of the story, but no one site can cover every aspect. So we're going to keep an updated list of the top stories and happenings throughout the day. (We'll put new links at the top.)

CSO describes an FBI official's claim that "We're chopping off the head of LulzSec," but says LulzSec is pretty small compared to the overall Anonymous movement. There's no reason to believe "that the hacktivist element of Anonymous will fall apart because of this," one security company executive notes.

The Guardian has posted the full text of some of the documents from the indictments against LulzSec members. The paper also has an analysis of the court papers, detailing Monsegur's cooperation with the FBI. The story notes Monsegur providing the FBI advance notice of attacks, which the FBI apparently allowed to proceed. "The FBI even provided its own servers for members of hacking collectives to use."

WikiLeaks tweeted a link to LulzSec chat logs from last August, saying the text shows "FBI informant Sabu tried to entrap anonymous hackers with $ for info."

Gawker has posted a story saying Monsegur was arrested on Feb. 3 in New York City by NYPD for attempting to pass himself off as an FBI agent.

Self-appointed Anonymous spokesman Barrett Brown told the New York Times that he received advance warning of the FBI raid on his home in Dallas, and that he hid his laptops to avoid them being found. Brown promised that "Anonymous will go forward as usual. So will I. We hired an army of lawyers last January. We are prepared for a big slug-out." (The quote seems to have been deleted from the Times story, although a portion of the quote exists in another Times article and the full quote appears in some other accounts.)

Fox News kicked it off this morning with an exclusive look into the FBI raid on Monsegur's New York apartment last June. Monsegur had normally been cautious, but slipped up one day when he "logged into an Internet relay chatroom from his own IP address without masking it." Fox News notes that "All it took was once. The feds had a fix on him."

Monsegur pleaded guilty on August 15 to conspiracy to engage in computer hacking, a plea only made public today.

Monsegur and five other members of Anonymous, LulzSec, and other groups were charged with various crimes including last year's famous attack against security firm HBGary Federal, and one against private intelligence firm Strategic Forecasting (or Stratfor), Bloomberg reports. In addition to Monsegur, Ryan Ackroyd, Jake Davis, Darren Martyn, Donncha O’Cearrbhail, and Jeremy Hammond were the names of the other alleged hackers. Other crimes pinned against some or all of the six defendants include attacks on Fox Broadcasting, the Chicago Tribune parent Tribune Co., and the government websites of Algeria, Yemen, and Zimbabwe.

The FBI press release has many details about the arrests and specific charges, saying the victims of the six hackers numbered over 1 million.

Barrett Brown said the arrested hackers formed the de facto leadership of Anonymous, and called Monsegur "an absolute traitor," the same Bloomberg story also notes.

FBI officials raided a Chicago home yesterday in connection with an investigation into the LulzSec and Anonymous hacking groups, the Chicago Tribune reports, citing an unnamed law enforcement source. The story does not say whose home was raided, but Bloomberg noted that Hammond was arrested in Chicago for crimes related to the Stratfor hack.

Consulting firm Errata Security has posted its own notes on the Sabu arrest, calling it "a good lesson for Tor users. Tor, itself, is not enough to keep your identity hidden." Monsegur was a Tor user, although he was caught after logging on to IRC without going through Tor.

The Anonymous Twitter account AnonOps sent out a terse message stating "@anonymouSabu is now controlled by feds. We have blocked the account and we suggest you do as well. #BlockAnonymouSabu."

Another Anonymous Twitter account promised to fight on in its own decentralized way, saying "We don't have a leader." A site called "Death and Taxes" downplayed the arrests' impact on Anonymous, noting that the belief that "Sabu" was a rat has been circulating in the hacking community for months. "Anonymous has grown beyond LulzSec and Sabu," the article states.

Before the indictment unsealing yesterday, the Twitter account allegedly run by "Sabu" tweeted "The federal government is run by a bunch of fucking cowards. Don't give in to these people. Fight back. Stay strong."

The Wikipedia page on Sabu has been updated to reflect Monsegur's arrest, and we'd imagine it will undergo quite an overhaul in the next few days.