"Sabu" was arrested in June 2011.
Prosecutors from US are seeking a lenient in sentence for a leader of LulzSec hacking group, Hector Xavier Monsegur, claiming that his cooperation and inputs helped in preventing more than 300 cyber attacks.
In a court filing, the New York prosecutors have provided the details of Monsegur's cooperation with the prosecutors and requested the judge to show leniency.
Monsegur, operating with the nickname "Sabu", was arrested in June 2011 and already pleaded guilty with charges of identity theft and credit card fraud.
He was heading a group called "Lulzsec," or Lulz Security, which went on high profile hacking spree during 2011, and after his arrest he admitted his role in hacking of companies such as HBGary, Fox Entertainment and Sony Pictures.
If convicted on the charges levelled against him, he could face up to 26 years in jail for causing losses of $2.5m through his hacking exploits.
The prosecutors claimed that Monsegur helped the FBI to prevent several attacks on websites of US military, NASA and other media companies.
The prosecutors said in the court filing, "Monsegur acknowledged his criminal conduct from the time he was first approached by agents, before he was charged in this case."
"Monsegur admitted both to prior criminal conduct about which the Government had not developed evidence, as well as his role in both Internet Feds and LulzSec.
Monsegur subsequently and timely provided crucial, detailed information regarding computer intrusions committed by these groups, including how the attacks occurred, which members were involved, and how the computer systems were exploited once breached.
The prosecutors also added that Monsegur's input helped directly in the identification, prosecution and conviction of eight of his major co-conspirators, including Hammond, who at the time of his arrest was the FBI's number one cybercriminal target in the world.
Monsegur help also helped FBI in nailing cybercriminals affiliated with Anonymous, Internet Feds and the information provided by him helped the agency in understanding the modus operandi, hierarchy and membership of the hacking groups, the prosecutors said.
The prosecutors plead before the judge that he should not be imprisoned more than seven months which he has already severed in 2012.