Hacker, Informant and Party Boy of the Projects In his Lower East Side apartment, the nights were racket-filled and without end. Neighbors lived with the pounding music and the sound of a pit bull being chased around the living room. The revelry sent scores of calls to the city's complaint line. In that same apartment he hatched the online plots, the ones intended to cripple the governments of Algeria and Zimbabwe, to shame some of the biggest brand-name companies in the world. On the Internet he was Sabu, a notorious celebrity who led a scattered tribe of politically motivated "hacktivists," revered as the sly mastermind of brash computer attacks. Then, when he was caught, he slipped into the role of federal informant. But always he was Hector Xavier Monsegur, party boy of the projects. The multiple worlds of Sabu converged on Tuesday when court papers revealed his real identity. As an informant, he helped bring down a batch of prominent fellow hackers in Europe and the United States. They were indicted on a charge of computer crimes that the authorities said affected one million victims, along with major companies and government agencies. Hackers, concealed behind fanciful aliases on the Internet, often appropriate larger-than-life dimensions. In reality, other than in physical proportions, Sabu seemed considerably smaller than life. A defensive-lineman-size man known as Booby, he was raising the two young children of his imprisoned aunt in a public housing project. Court documents showed that Mr. Monsegur, 28, paid bills with stolen credit cards and dabbled in drug sales. In one neighborly gesture, he offered to use his hacking skills to sweeten other tenants" credit ratings. On Twitter, both before and after he was helping the authorities catch his compatriots, he was prone to grand declarations: "Give us liberty or give us death - and there's billions of us around the world. You can't stop us. Because without us you won't exist. In the days before his unmasking, he was strangely haunted by the subject of turncoats. "So you're telling me if you get locked up, and your nosy neighbor who dropped the dime on you runs free - you would simply ignore?" he posted Monday. Mr. Monsegur's whereabouts are unknown, and his lawyers declined to comment. His background remains gauzy, but court records and interviews with relatives and neighbors offer an outline. He was born in 1983. His father, also named Hector Monsegur, was arrested in 1997 along with his sister, Iris, for selling heroin. Both went to prison for seven years. While his father was locked up, Mr. Monsegur apparently moved in with his grandmother, Irma, who lived in a sixth-floor apartment in the Jacob Riis Houses, a Lower East Side housing project. School officials said Mr. Monsegur attended Washington Irving High School, but left in 2001 without finishing ninth grade. In the transcript of his guilty plea, Mr. Monsegur said that he went to college, though it is unclear if he actually did. After his release from prison in early 2003, Mr. Monsegur's father found work with a sanitation company. The aunt, Iris, ran a credit repair company from her Staten Island home. Her involvement with drugs, however, continued. She was arrested again and returned to prison in 2010. By that point she had had two girls. They were entrusted to the care of the younger Mr. Monsegur, and he gained legal custody of them. Even after his aunt left prison last August, her children remained with Mr. Monsegur. He worked sporadically, including for a few months at OpenPlans, a nonprofit group that tries to improve government through technology. His profile on the networking site LinkedIn, which listed him as a senior systems administrator there, disappeared on Thursday. A former co-worker described him as friendly and competent. But authorities said he had been unemployed in recent years. Reporting was contributed by William Rashbaum, Nicole Perlroth, Tim Stelloh, Alex Vadukul, Toby Lyles and Jenny Anderson.