Words of Authority: Evaluating the Impact of Law Enforcement Messaging on a Hacker Forum

Law-enforcement agencies increasingly target individuals considered at risk of cybercrime, yet evidence of these interventions’ effectiveness remains limited. This study evaluated an intervention in which law enforcement publicly replied to hacker-forum users with warnings about cybercrime and legitimate alternatives. Using a retrospective matched design, we compared 143 treated users with 286 similar controls. We examined whether treated users subsequently reduced, delayed, or desisted from blackhat posting or shifted towards whitehat posting more than controls. Blackhat posting declined after targeting, but controls showed a similar decline. Treated users also did not delay, desist, or shift towards whitehat participation more than controls. Exploratory analyses including users unnotified of targeting indicated increased blackhat posting, faster return, and less desistance among treated users. These findings demonstrate the importance of suitable comparison groups and careful attention to targeting, message delivery, and possible unintended responses when evaluating online police interventions.