A prominent hacker set to be sentenced in federal court this week for breaking into numerous computer systems worldwide has provided a trove of information to the authorities, allowing them to disrupt at least 300 cyberattacks on targets that included the United States military, Congress, the federal courts, NASA and private companies, according to a newly filed government court document.

The hacker, Hector Xavier Monsegur, also helped the authorities dismantle a particularly aggressive cell of the hacking collective Anonymous, leading to the arrest of eight of its members in Europe and the United States, including Jeremy Hammond, who the Federal Bureau of Investigation said was its top “cybercriminal target,” the document said. Mr. Hammond is serving a 10-year prison term.

The court document was prepared by prosecutors who are asking a judge, Loretta A. Preska, for leniency for Mr. Monsegur because of his “extraordinary cooperation.” He is set to be sentenced on Tuesday in Federal District Court in Manhattan on hacking conspiracy and other charges that could result in a long prison term.

It has been known since 2012 that Mr. Monsegur, who was arrested in 2011, was acting as a government mole in the shadowy world of computer hacking, but the memorandum submitted to Judge Preska late on Friday reveals for the first time the extent of his assistance and what the government perceives of its value. It also offers the government’s first explanation of Mr. Monsegur’s involvement in a series of coordinated attacks on foreign websites in early 2012, though his precise role is in dispute.