The Anonymous hacktivist sentenced on Friday to 10 years in federal prison for his role in releasing thousands of emails from the private intelligence firm Stratfor has told a Manhattan court that he was directed by an FBI informant to break into the official websites of several governments around the world.

Jeremy Hammond, 28, told a federal court for the southern district of New York that a fellow hacker who went under the internet pseudonym “Sabu” had supplied him with lists of websites that were vulnerable to attack, including those of many foreign countries. The defendant mentioned specifically Brazil, Iran and Turkey before being stopped by judge Loretta Preska, who had ruled previously that the names of all the countries involved should be redacted to retain their secrecy.

Within a couple of hours of the hearing, the three countries had been identified publicly by Forbes, the Huffington Post and Twitter feeds serving more than a million followers. “I broke into numerous sites and handed over passwords and backdoors that enabled Sabu – and by extension his FBI handlers – to control these targets,” Hammond told the court.

The 28-year-old hacker has floated the theory in the past that he was used as part of an effective private army by the FBI to target vulnerable foreign government websites, using the informant Sabu – real name Hector Xavier Monsegur – as a go-between. Sabu, who was a leading figure in the Anonymous-affiliated hacking group LulzSec, was turned by the FBI into one of its primary informants on the hacker world after he was arrested in 2011, about six months before the Stratfor website was breached.

Referring to the hacking of foreign government websites, Hammond said that in one instance, he and Sabu provided details on how to crack into the websites of one particular unidentified country to other hackers who then went on to deface and destroy those websites. “I don’t know how other information I provided to [Sabu] may have been used, but I think the government’s collection and use of this data needs to be investigated,” he told the court

He added: “The government celebrates my conviction and imprisonment, hoping that it will close the door on the full story. I took responsibility for my actions, by pleading guilty, but when will the government be made to answer for its crimes?”

Hammond’s 10-year federal prison service makes it one of the longest punishments dished out for criminal hacking offences in US history. It joins a lengthening line of long jail terms imposed on hackers and whistleblowers as part of the US authorities’ attempt to contain data security of government agencies and corporations in the digital age.