The founder of an offshoot of the shadowy hacker group Anonymous, who directed hundreds of cyber attacks before turning FBI informant, walked free Tuesday after getting a symbolic seven-month sentence.

Hector Xavier Monsegur, 30, better known by his screen name "Sabu," was first arrested in 2011 and had already served seven months in jail before being released on bail in December 2012.

Monsegur founded a group called "LulzSec," an offshoot of the loosely organized hacker community known as Anonymous, which carried out hundreds of cyber attacks on corporations and foreign governments, including one against the security firm Stratfor.

The original charges could have landed him in prison for decades but the government asked for him to be exempt from even a mandatory minimum sentence given his "extraordinary cooperation."

Before walking out of the US federal court a free man, he told Judge Loretta Preska that he did not intend to be back.

"I came a long way I assure you... I am not the same person I was," he said, wearing a black sport shirt.

Sabu and fellow plotters carried out hacks that cost companies tens of millions of dollars, defaced websites and stole personal information of customers or employees, court papers said.

The victims included MasterCard, PayPal and other commercial and government targets.

- Turning informant -

After his arrest he became a Federal Bureau of Investigation informant, helping to foil or limit 300 cyber attacks that could have caused millions of dollars of damage, prosecutors said.

His information also led to multiple arrests and sentencings of hackers, they added.

According to a report filed by prosecutors, Monsegur could have received 259 to 317 months in prison, but the government recommended leniency because he "was an extremely valuable and productive cooperator."

"He provided detailed historical information about the activities of Anonymous, contributing greatly to law enforcement's understanding of how Anonymous operates," the document said.

"Monsegur also provided crucial and detailed information about the formation, organization, hierarchy and membership of these hacking groups, as well as specific information about their planning and execution of many major cyber attacks, including the specific roles of his co-conspirators in committing those crimes."

He pleaded guilty to nine counts of computer hacking and one count each of credit card fraud, conspiring to commit bank fraud and aggravated identity theft.

He had admitted to being involved in cyber attacks on MasterCard, PayPal and Visa and on the Algerian, Tunisian, Yemeni and Zimbabwean governments.

He set up Anonymous offshoot Lulz Security, or LulzSec, which in 2011 engaged in major hacks into and theft from computer servers of US and foreign corporations.

Its victims included Fox Television, compromising a database of contestants in reality show "X-Factor," the website of US public broadcaster PBS, the US Senate and an affiliate of the FBI.

The New York Times reported last month that he directed hundreds of cyber attacks against the websites of governments in Brazil, Iran, Pakistan, Syria and Turkey.

It was unclear who ordered the attacks, but the newspaper said court documents and interviews suggest the government "may have" used hackers to gather intelligence overseas.

Monsegur instructed fellow hacker Jeremy Hammond, who was sentenced to 10 years in jail by a US federal judge last November, to extract data from foreign government websites.

Court documents showed that the FBI was monitoring Monsegur's communications with Hammond, described by officials as "the FBI's most wanted cyber criminal in the world at the time of his arrest."

But some of Monsegur's former collaborators were bitter about the sentence.

"Jeremy Hammond is serving a ten-year sentence for hacks that Sabu (working for the feds) told him to do. When will the feds go to prison?" said a tweet from Anonymous.