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Prosecutors: Hacker aided FBI

NEW YORK — A computer hacker who infiltrated major corporations later switched sides and helped the government disrupt hundreds of cyberattacks on Congress, NASA, and other sensitive targets, federal prosecutors said.

They 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 him with helping them cripple Anonymous, “hacktivists” who stole confidential data, defaced websites, and temporarily put some victims out of business.

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Monsegur provided “information about then-ongoing computer hacks and vulnerabilities in significant computer systems,’’ prosecutors wrote. The FBI estimates he helped prevent millions of dollars in losses. After his 2011 guilty plea, he faced two decades behind bars; now, the sentence could be two years or less.

Monsegur led an Anonymous splinter group called Lulz Security. Reports he was cooperating with the FBI made him a pariah in the movement, and harassment prompted the government to relocate him.

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