A top hacker who worked closely with LulzSec leader Sabu is a committed anarchist who mocked the 9/11 attacks, spoke of burning down the White House and ridiculed pacifist protesters for not using violence to achieve their means, FoxNews.com has learned.

Jeremy Hammond, whose online handles “Anarchaos” and “crediblethreat” and “tylerknowsthis” underscored his virulent anti-government beliefs, was arrested up Tuesday in Chicago as part of an international sweep netting top members of the hacker group LulzSec and its affiliates. The 27-year-old is a self-styled anarchist whose admirers call a modern day Robin Hood. He took credit for the massive attack on the global intelligence company Stratfor and even embraced being branded a “terrorist” in a speech at a 2004 hacker convention caught on video.

“One man’s freedom fighter is another man’s terrorist,” Hammond told the audience at the annual DefCon hackers conference in Las Vegas 2004. “So let them call us terrorists,” he added moments later. “I’ll still bomb their buildings.”

The tough talk is in sharp contrast to the image some have of LulzSec as a merry band of Internet mischief-makers. Hackers in the group were stunned on Tuesday when FoxNews.com broke the story that LulzSec’s leader, Hector Xavier Monsegur, known to his minions as “Sabu,” had been secretly working for the FBI after being arrested. Chat logs included in Hammond’s indictment purport to show Hammond and Sabu’s numerous online conversations; in some, Hammond talks about the Stratfor hack and his previous arrests and time spent behind bars. But even prison time did nothing to soften Hammond’s angry worldview.

“This guy is not some harmless kid living in his parents’ basement,” a law enforcement source said of Hammond. “He’s got a history and potential for violence.”

Chilling chatroom transcripts obtained by FoxNews.com capture the dark and disturbing views of Hammond, whose mother said he has an IQ of 168 and called him a “genius without wisdom,” in a Chicago Tribune interview. In the discussions with an unknown audience, Hammond hailed the 2007 book “How Nonviolence Protects the State,” by self-proclaimed anarchist Peter Gelderloos, praising it for encouraging violence and sabotage.

“I didn't start the conversation about burning the white house, but I'll finish it,” vowed Hammond in one undated post.

In another post, Hammond calls for “organized, coordinated attacks against targets who are more directly responsible for our miserable conditions,” and proposes “a toast to the rich! with our choice of cocktail.”

Perhaps most disturbing is this chilling dialogue about 9/11:

“So what's the best way to celebrate 9/11? A jenga tournament!” Hammond posted. “We played a big 9/11 show on saturday, we had a pinata of the world trade towers … it was filled with candy and miniature plastic army men.”

In response to a request for comment, Hammond's attorney Jim Fennerty told FoxNews.com via e-mail, "I know nothing about his postings on line."

In 2005, Hammond formed a group he dubbed the “Internet Liberation Front.” He hacked into a conservative website and stole 5,000 credit card numbers which he intended to use to make donations to liberal causes, according to authorities. Although he was caught before he could carry out the plan, which prompted comparisons to Robin Hood, he served two years in prison.

Hammond was arrested again in 2010 he was arrested for allegedly throwing a banner into a fire at a protest against the Olympics coming to Chicago. He was given 18 months probation.

Authorities believe Hammond was the main player in the Stratfor hack last December, in which 5 million emails were stolen and handed over to Wikileaks. According to the federal complaint against Hammond, the attack was designed to bankrupt Stratfor, a Texas-based company that works with intelligence agencies around the world. This time, Hammond is facing up to 10 years in prison.

“The sheer amount of destruction we wreaked on Stratfor’s servers is the digital equivalent of a nuclear bomb: leveling their systems in such a way that they will never be able to recover,” wrote a LulzSec member in an online post.