A computer hacker who infiltrated the servers of major corporations defected to the men in suits to avoid a large jail sentence.
Hector Xavier Monsegur was arrested by the cops and it was likely he would get more than 20 years porridge under the US government's "lock em up for years for no real purpose" justice system.
However Monsegur switched sides and helped the government disrupt hundreds of cyberattacks on Congress, NASA and other sensitive targets.
New York prosecutors detailed the cooperation of Monsegur for the first time in court papers while asking a judge to reward him with leniency at his sentencing Tuesday.
Monsegur helped them cripple Anonymous and worked around the clock with FBI agents at his side.
He provided, in real time, information about then-ongoing computer hacks and vulnerabilities in significant computer systems, prosecutors wrote.
The FBI estimates he helped detect at least 300 separate hacks, preventing millions of dollars in losses, they added.
It is believed that despite saving the Land of the Fee more than 300 times, he will still face jail. But because of his cooperation, the sentence could be two years or less.
However in a 2011 interview with an online magazine, Monsegur said he decided to join forces with Anonymous because he was upset over the arrest of WikiLeaks founder Julian Assange.
Using the alias Sabu, Monsegur led Lulz Security, or LulzSec, which hacked computer systems of Fox television, Nintendo, PayPal and other businesses, stole private information and then bragged about it online.
When arrested Monsegur immediately agreed to cooperate, giving the FBI a tutorial on the inner-workings and participants of LulzSec and Anonymous, prosecutors said. Under their direction, he "convinced LulzSec members to provide him digital evidence of the hacking activities" and "asked seemingly innocuous questions that ... could be used to pinpoint their exact locations and identities," court papers said.
Reports that Monsegur was cooperating made him a pariah in the Anonymous movement, prosecutors said. Hackers began posting personal information about him, and he was even approached on the street and threatened, they said. He, and his family were later placed in a witness protection programme