No fewer than 300 American sympathizers are helping the Islamic State terrorist group recruit potential members and spread propaganda via Twitter, according to a new report from George Washington University's Program on Extremism. The report drew on court records, media reports, interviews and other sources to find that U.S. supporters of the group, aka ISIS, “spasmodically create accounts that often get suspended in a never-ending cat-and-mouse game.”

The FBI has increased its surveillance of known ISIS supporters in the U.S. since terrorist attacks claimed 130 lives in Paris last month. 56 Americans have been arrested on ISIS-related charges this year, the Wall Street Journal reported, and concern about the group's influence has grown since ISIS expanded its breadth of attacks. Now, in a report published Tuesday, researchers have pointed out hundreds of Twitter users based in the U.S. who are helping ISIS spread its message, including a number who “cultivated and later strengthened their interest in ISIS' narrative through face-to-face relationships.”

Researchers tracked users by using Twitter's geolocating tools, analyzing their use of language or cultural references and found many who self-identified as Americans, either in their Twitter handle or in their conversations. Roughly one-third were women, and both sexes tended to use black flags or other ISIS iconography in their avatars. Experts warned that while not all of those identified pose threats to U.S. national security, American ISIS supporters tend to congregate in small cells that are difficult for authorities to identify.

“Some of the most important intelligence is no longer secret,” Jane Harman, president of the Woodrow Wilson International Center for Scholars, wrote in an introduction to the report, as quoted by CBS News. “Some of the best information is open-source, plastered on message boards or a 19-year-old's Twitter feed. Policymakers have been slow to adapt; spies would still rather squint at satellite photos than scrape Facebook feeds.”