Eighteen months after Facebook banned communities and users connected with the “Boogaloo” anti-government movement, the group’s extremist ideas were back and flourishing on the social media platform, new research found.

The paper, from George Washington University and Jigsaw, a unit inside Google that explores threats to open societies — including hate and toxicity, violent extremism and censorship — found that after Facebook’s June 2020 ban of the Boogaloo militia movement, the content “boomeranged,” first declining and then bouncing back to nearly its original volume.

“What this study says is, you can’t play whack-a-mole once and walk away,” said Beth Goldberg, Jigsaw’s head of research and development. “You need sustained content moderation — adaptive, sophisticated, content moderation, because these groups are adaptive and sophisticated.”