The FBI has apparently turned "Sabu," who was the mastermind behind the pranksterish hacking group LulzSec, an Anonymous offshoot that went on a frenetic corporate hacking spree last summer. A handful of LulzSec members were taken into custody in the US and UK today as a result of Sabu's help.

Fox News has the story, from a law enforcement source, of how two FBI agents climbed the stairs to a sixth-floor apartment last summer in a New York public housing development and found 28-year old Hector Monsegur, the unemployed man behind the handle "Sabu." Worried about the fate of two children in his charge, Monsegur has allegedly been aiding the FBI since his arrest last summer—aid which culminated in arrests today of several LulzSec members.

Monsegur's federal court docket remained sealed until this morning. The documents themselves aren't yet available, but the docket indicates that he was arrested on June 7, 2011 and the next day was released on $50,000 bail. "Deft to be supervised by the FBI with respect to travel and reporting and all other issues," noted the court. Monsegur later pleaded guilty to some of the charges levied against him.

Despite Monsegur's status as a high-profile hacker, he had little money, living in public housing and using a public defender for a lawyer.

The strange twist isn't a total surprise; rumors have circulated for months that Sabu had been turned by the feds, and his identity was successfully exposed online several times already (a process known as "doxing" within Anonymous circles).

Fox was given access to Sabu's handlers, who revealed that he was online between 8 and 16 hours a day and was watched by monitoring software and by an agent who supervised "his online activity 24 hours a day."

For the last nine months, Sabu has tweeted, hacked, and acted at the FBI's direction, helping to reveal other members of LulzSec and to sow disinformation at the FBI's request.