The “CyberCaliphate” hacking ring that took over a Pentagon Twitter account on Monday is reportedly led by a 20-year-old British man who moved to Syria to help jumpstart ISIS’s hacking efforts. Junaid Hussain, the man named in a Reuters report, was once jailed for hacking the address book of Prime Minister Tony Blair.

Junaid Hussain is believed by U.S. and European government investigators to be the leader of CyberCaliphate, but it is unclear if he was directly behind the attack, the report said. The hackers took over Twitter and YouTube accounts belonging to U.S. Central Command, or CENTCOM, often used to provide updates about airstrikes against ISIS.

CENTCOM oversees U.S. military actions in the Middle East, but the Pentagon said that no classified or sensitive information was compromised in the attack. Spokesman Army Colonel Steve Warren has said the attacks were “inconvenient and an annoyance. But that’s all it is.”

Hussain is in charge of recruiting hackers for the Islamic State’s digital terrorism efforts, analyst Alex Kassirer from Flashpoint Global Partners told Reuters. Flashpoint, a private company, monitors extremist message boards and websites.

The CyberCaliphate first surfaced when it posted recruitment advertisements on extremist sites, Kassirer told Reuters. She also said that Hussain’s wife claimed last week that he had been killed in drone attacks, but officials told the news agency there was no confirmation Hussain was dead.

British media reports said Hussain planned to hack the bank accounts of the U.K.'s "rich and famous" to fund ISIS exploits. He lived in Birmingham, England, before moving to Syria sometime after his 2012 arrest for hacking the prime minister’s address book. He pleaded guilty to posting it online, serving six months in jail.

Investigators told Reuters they were trying to determine whether the CENTCOM hack originated from Syria. They believe that Hussain was the main user of a Twitter account linked to the CyberCaliphate that was suspended on Tuesday.