“Mr. Hussain wore a number of hats, including that of a hacker. He was linked to the release of personal information on more than 1,300 American military and government employees. In March 2015, his group posted the names and addresses of service members with instructions: ‘Kill them in their own lands, behead them in their own homes, stab them to death as they walk their streets thinking they are safe.’ More important were Mr. Hussain’s efforts as an online recruiter. According to court records, Mr. Hussain communicated with at least four men in four states, imploring them to initiate attacks...