NEW YORK (AP) — A prolific computer hacker who infiltrated the servers of major corporations later switched sides and helped the government disrupt hundreds of cyberattacks on Congress, NASA and other sensitive targets, according to federal prosecutors.

New York prosecutors detailed the cooperation of Hector Xavier Monsegur for the first time in court papers while asking a judge to reward him with leniency at his sentencing Tuesday. They credited Monsegur with helping them cripple Anonymous, the notorious crew of hacktivists who stole confidential information, defaced websites and temporarily put some victims out of business.