Former LulzSec and Anonymous member Jeremy Hammond has pleaded guilty to hacking intelligence firm Stratfor to expose millions of emails.

The Illinois man could face up to ten years in prison when he is sentenced in September. As part of his plea deal, Hammond, who was involved with Anonymous and offshoot LulzSec, accepted responsibility for infiltrating a number of other intelligence-related sites, including equipment suppliers and police agencies. He had been publicly accused of illegally accessing the Arizona Department of Public Safety.

In a statement posted on his support website, Hammond said that by pleading guilty, he is protected from being prosecuted for the other offences. “Even if I was found not guilty at trial [in New York], the government claimed that there were eight other outstanding indictments against me from jurisdictions scattered throughout the country,” he wrote.

“If I had won this trial, I would likely have been shipped across the country to face new but similar charges in a different district. The process might have repeated indefinitely.”

Hammond also stated that he was proud he shed light on the secret dealings of Stratfor, which serves major corporate and government agency clients. “Now that I have pleaded guilty it is a relief to be able to say that I did work with Anonymous to hack Stratfor, among other websites,” Hammond wrote.

“I did this because I believe people have a right to know what governments and corporations are doing behind closed doors. I did what I believe is right.”

Prosecutors have said that in addition to the emails, Stratfor hackers also stole 60,000 credit card numbers from clients to make unauthorised charges totalling £700,000, in addition to the personal information, such as names and email addresses, of 860,000 people. Much of the charges were reportedly made on behalf of charities.

Stratfor said the hack cost it millions, including nearly $2 million to settle a class-action lawsuit brought by members. Supporters of Hammond have launched a petition asking that Judge Loretta Preska sentence Hammond to time served.

Authorities arrested Hammond after he was named by former Anonymous and LulzSec member Hector ‘Sabu' Monsegur, who worked as an FBI informant after his arrest. His LulzSec co-defendants were recently sentenced in the UK.