A Hacker Charms and Disappoints

Hector Xavier Monsegur, or Sabu, lived in Apartment 6F at 90 Avenue D in the Jacob Riis complex in Manhattan.Robert Stolarik for The New York TimesHector Xavier Monsegur, or Sabu, lived in an apartment on Manhattan’s Lower East Side.

Skilled, profane and bombastic, the hacker who called himself Sabu had loyalists and critics. He also had admirers who marveled at his antics from afar, even as they disdained his tactics. That admiration helped explain the attraction of the Anonymous movement that Sabu came to represent.

Nadim Kobeissi, a college student, security software developer and self-described activist in defense of free speech on the Internet, was among his admirers. He did not know the offline identity of Sabu, who last week authorities revealed to be Hector Xavier Monsegur, a 28-year-old resident of the Lower East Side. Court papers identified him as an informant in a federal indictment against a group of hackers aligned with Anonymous.

Mr. Kobeissi did not agree with most of Sabu’s tactics, like extracting names and credit card numbers of unsuspecting citizens. He did consider himself a fellow traveler in the sense that, like Sabu, he too opposed government censorship. He appreciated Sabu’s idealism, his swagger.

He was thrilled, he said, to receive compliments from Sabu on Twitter. In recent months, Mr. Kobeissi recalled, Sabu praised his coding skills, and vaguely invited him to join him on his escapades. Mr. Kobeissi was pleased by the praise, he said, though less than eager to engage in an attack.

“I thought it was cool, ” Mr. Kobeissi said by phone from Montreal this week, after news broke of Sabu’s arrest and cooperation with the federal authorities. “Sabu thinks I’m cool. That’s nice!”

Sabu had a rare cred. He was sharp tongued, and he used a Hamas flag as his Twitter avatar. In the coder circles that Mr. Kobeissi runs in, Sabu was widely credited as the mastermind of several high-profile hacks that an Anonymous offshoot, LulzSec, took credit for – most famously, the attack on the security firm HBGary Federal. He was also known for showing off about his hacks in the most spectacular ways. LulzSec, for instance, publicized the HBGary hack on its Web site with the theme song to “The Love Boat,” except it was called the Lulz Boat.

“The image he gave off and he did it very well, even after he was arrested by the F.B.I., he seemed like a very determined idealistic sort of person,” Mr. Kobeissi said. “He seemed to care about a bunch of things and wouldn’t stop at anything.”

“He could be so obnoxious!” Mr. Kobeissi added. It was a compliment.

Only recently did Mr. Kobeissi realize that Sabu was trying to trick him – and that Sabu had, for more than six months, been helping the federal authorities track down his compatriots in Anonymous. Mr. Kobeissi immediately posted links to the news on his Twitter page. The next day, he issued a warning to others who may be seduced in the future.

“Sabu repeatedly encouraged me to work with him,” he wrote. “Please be careful of anyone ever suggesting illegal activity, even if they do it with you.” That message was shared widely.