"I'm pissed off," the notorious hacker Sabu told me on the phone last September, lamenting the latest arrests in a worldwide crackdown on the hacking collective Anonymous. "I'm getting real sad, with all the bullshit. It's all media hunger on the side of the FBI, my nigga."

I learned today that when Sabu said all this during an unexpected phone conversation last fall, he was also on the side of the FBI as an informant. 28-year-old Hector Monsegur—a.k.a. "Sabu"—was arrested last June. He pleaded guilty to 12 hacking charges in August and turned informant, helping feds take down members of LulzSec, the Anonymous off-shoot he had once led. Today, thanks to evidence he collected, five of Sabu's former associates were arrested. But he did a pretty good job of playing the underground king when I talked to him, even if, in all likelihood, the feds were listening in and he knew it.

Nothing is ever straightforward about hackers, and the way I ended up talking to Monsegur was typically convoluted. Last fall I came across a phone number said to belong to Sabu; I'd chatted with him on and off while reporting on his and his associates' hacks, but only over the Anonymous chat networks on which he was a constant presence. As far as I knew, no non-hacker had ever heard his voice.

(Our conversations were off the record; we decided to go ahead with publishing the details today after learning that he'd been an informant at the time we spoke.)

I called the number once a day for maybe two weeks, each time reaching a default voicemail message until one day a guy—sounding in his mid-30s, with a thick New York accent—answered; from the clamor of voices and music in the background, he might have been in a crowded bar. He didn't sound like an Anonymous member, those geeky white teen recluses who were being rounded up by the dozen and proving all the hacker stereotypes correct.

I told him who I was, and who I thought he was: A famous hacker named Sabu, leader of a group called LulzSec who had hacked Sony, PBS, Fox News, etc. over the summer. Was that you?

"Who the fuck are you," he said, and hung up.

But a few days later, on Sept. 21, I got a chat from Sabu: "You find my voice sexy?" he wrote. "You kept calling my fucking Skype number every day. What was wrong with you?"

"I was trying to figure out who that phone number belonged to. Why did you pretend not to be Sabu?" I asked.

"I fucked with you purposely son… I honestly didn't want to talk to you. I got more important shit going on (family, et al.)" Monsegur has two kids, one major reason he turned informant.

"It was because of his kids," one agent told Fox News. "He'd do anything for his kids. He didn't want to go away to prison and leave them. That's how we got him."

The next day we had a real chat on the phone. Sabu let loose a half-hour rant about the corruption of the Feds we now know he was working for, and the downfall of his comrades we now know he was actively aiding. It was a strange time for Sabu: he'd recently re-appeared after mysteriously dropping off the scene for a couple months—now it's apparent this was when he was being turned—and rumors swirled that he was working for the feds, which he vigorously denied.

"That's bullshit," he scoffed. "I stop posting on Twitter and mad rumors get started."

And as an increasing number of Sabu's former associates fell over the summer, other detractors accused him of using these inexperienced hackers as human shields who got busted while he safely reaped the glory of their hacks. But he told me their inexperience just proved that the feds would arrest any two-bit script kiddie to put on a show.

"They're little kids, they're nerds. They're not from the streets," he said. "They're not prepared for it. They think that because they're hiding behind a proxy they're money."

Sabu thought he was different. "I come from the streets. I'm not scared of jail," he boasted to me.

According to court papers, Mongsegur hacked out of a Lower East Side public housing development called the Jacob Riis Houses—the same development his parents had reportedly been kicked out of in 1997, after they were caught selling heroin. He loved cars and apparently had a YouTube account—LeSTerrorist—dedicated to street racing videos. The federal indictment against him alleges he hacked an auto parts company and sent himself four engines worth over $3,000.

Sabu took as much pride in his street cred as he did his long history of hacking: "I come from efnet 10 years ago doing operations in China," he boasted. "Doing Hackweiser," a legendary hacking group from the late 90s and early 2000s. It's unclear how prolific Monsegur really was, but the net is littered with traces of a hacker named "Sabu" who defaced websites in protest of U.S. bombing exercises in Puerto Rico back in the early 2000s.

But Sabu saved the most ire for informants, without which he claimed the FBI "wouldn't have shit."

"That little faggot is from Tennessee," he said last September, about one rival hacker he accused of snitching. "Out there straight up getting immunity for snitching niggas out." This seems now to have been an attempt at muddying the waters, given reports that the Feds used Sabu to spread disinformation to journalists.

In our phone chat, Sabu also hinted at outlandish hacks he and his crew had carried out and were waiting to unleash on the world. "You know how much power I have in my hands?" he asked at one point. "I don't mean to sound like an egomaniac. We have fucking control of SCADA systems. We have control of entire ISPs. We have banks, my nigga."

At the time, I wrote this off as the empty boasting typical of the hacker underground. But Monsegur's FBI handlers couldn't have been too disappointed if, after a tip from their best asset, an article had appeared soon after, pumping up the threat of the very hackers they were quickly closing in on.