They say his help in preventing the loss of millions of dollars should earn him leniency when he is sentenced on 27 May 2014 for his role in major hacking attacks, reports the BBC.
Monsegur has admitted involvement in cyber attacks in 2011 against the media groups Sony Pictures Entertainment, Fox Broadcasting Company and the Public Broadcasting Service (PBS).
LulzSec was formed in around May 2011 when Monsegur - also known as Sabu - and five other members of the Anonymous hacktivist collective joined forces.
Since his arrest, Monsegur has helped prevent major hacking attacks against military, government and commercial targets. He has aided the FBI in several key arrests, prosecutions and convictions in the US, UK and elsewhere, including Anonymous member and US cyber crime kingpin Jeremy Hammond, for an attack on the Stratfor security think tank in 2011.
Read more about LulzSec
- US indicts suspected UK LulzSec member
- Feds announce Anonymous, LulzSec arrests
- LulzSec returns to target Murdoch
- Hackers attack Panda Labs website in LulzSec revenge attack
- FBI informer Hector Xavier Monsegur aids in arrest of LulzSec hackers
- Suspected LulzSec hacker named and charged
- Suspected teen LulzSec hacker released on bail
- UK police nab another suspected LulzSec teen hacker
- Anonymous and LulzSec hackers hit Italian cyber crime unit
- FBI makes LulzSec arrests in Sony breach investigation
Monsegur is also credited with exposing a hoax attack on the US power grid and telling US authorities about vulnerabilities that could have led to attacks on a water utility for a US city and a foreign energy company.
Monsegur faces a prison sentence of up to 26 years, but prosecutors have recommended that his sentence is limited to time served.
He has spent seven months in jail after breaking the conditions of his bail in 2012.