Much of ISIS’ ideology is disseminated through social media. According to a Brookings report, The ISIS Twitter census: Defining and describing the population of ISIS supporters on Twitter, by J.M. Berger and Jonathan Morgan, there were at least 46,000 users in October-November through 2014, with one in five users speaking English. Many of ISIS followers tweet at rapid rates.

Though many of those accounts are frequently suspended, the online community survives because of the “whack-a-mole” effect. When one account dies, other supporters direct followers to the new accounts of previously suspended users.

But it’s not just the flashy and extensive ISIS propaganda machine that attracts followers. Berger says most of ISIS’ success is due to the high level of personal engagement. “ Circles of users will surround a potential recruit and get involved not just directly but with the recruit’s other social networks, for instance trying to insulate them against unwanted attention by outsiders,” explained Berger in an email.

Recruiters include both fighters and supporters overseas, he says, “They’re patient, and will interact with a potential recruit over a long period of time if necessary, sometimes steering them in the direction of a particular kind of action.”