Junaid Hussain, a British citizen of Palestinian origin living in Birmingham, had one talent: Hacking. And when that special gift was coupled with radical ideology, it produced one of the most dangerous terrorists to emerge during the Global War on Terror. Because of his technological genius and strategic mind, Hussain quickly rose through the ranks of the terrorist organisation, becoming the No. 3 leader of ISIS. The 21-year-old hacker became one of the most wanted men in the world. The U.S. government put Hussain on its most wanted list because of his ability to encourage homegrown lone-wolf attacks in the West.

According to John P. Carlin, a former Assistant Attorney General for National Security under the Obama administration, Hussain was responsible for countless attack plots against the United States. In a book describing the fight against foreign cyberwarfare threats called Dawn of the Code War: America’s Battle Against Russia, China, and the Rising Global Cyber Threat, Carlin says that “Nearly every week of 2015 brought a new Hussain-inspired plot against the United States; FBI surveillance teams were exhausted, chasing dozens of would-be terrorists at once.”

Hussain was responsible for tweeting a kill-list containing the names and information of 1,351 U.S. military or government personnel. His threat, however, stemmed from his ability to motivate and coordinate aspiring terrorists on American soil. He communicated with multiple individuals — many who attempted terrorist attacks — and advised them. For example, he instructed and helped, by providing addresses, Munir Abdulkader, a 21-year-old from Cincinnati, to abduct and behead U.S. soldiers stationed in Ohio.

“Within the government, alarm bells rang daily, but we attempted to downplay the threat publicly,” writes Carlin. “We didn’t want to elevate Hussain to another global figurehead like Osama bin Laden, standing for the twisted ideology of Islamic jihad.”

But it was hard to track him down. Hussain bragged in an interview taken in ISIS-held territory that he was certain that the Western intelligence services didn’t have any information on him. “I don’t exist to them, I’ve never used my real details online, I’ve never purchased anything. My real identity doesn’t exist online — and no, I don’t fear getting caught.”

Despite his claims, the U.S. intelligence agencies knew about him. But they were so concerned about making Hussain a symbol of martyrdom that they didn’t publicly mention him until his death. “We debated in our daily briefings how public we should be about his role — we needed to focus government resources on him but didn’t want to make him 10,000 feet tall, a hero to his own cause.”

Eventually, however, the terrorist was located. The manner by which Hussain guaranteed his safety highlights his perverse mind: Keeping his young stepson with him at all times, the ISIS terrorist ensured that U.S. missiles would be hard to strike him — given the Rules of Engagement (ROE) by which American and allied warfighters must comply. One night, however, he was caught off-guard, leaving an internet café without his human shield. Moments later, a Hellfire missile killed him as he was refueling his vehicle.