ASYMMETRIC WARFARE, AMERICAN-STYLE: One by One, ISIS Social Media Experts Are Killed as Result of F.B.I. Program.

While American and British forces conducted a series of drone strikes on members of the group, the F.B.I. sifted through thousands of the Legion’s followers on social media to figure out who had actually been inspired to take action. In the last two years, it has arrested nearly 100 people in cases involving the terrorist group.

Several of the arrests were of people who had direct contact with the Legion. Many of the others involved were “folks who first came on our radar because we became aware of them” through their connections with Hussain and Reyaad Khan, also a British citizen, who was another leader of the group, according to Andrew McCabe, deputy director of the F.B.I.

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 or help spread the Islamic State’s message. Mr. Hussain was behind a plot to behead Pamela Geller, the author of a conservative blog. In early 2015, Mr. Hussain began communicating with Usaamah Abdullah Rahim, 26, and gave him instructions to kill Ms. Geller.

Mr. Rahim abruptly abandoned the plan and decided instead to kill a police officer in the Boston area. The bureau was monitoring him, and Mr. Rahim was shot and killed in June 2015 after he confronted an F.B.I. surveillance team with a knife. The F.B.I. also arrested two of Mr. Rahim’s associates, whom prosecutors say were involved in the plot.

Faster, please.