A bug in Facebook’s software resulted in the personal profiles of more than 1,000 content moderators being viewed by members of Facebook groups that included potential terrorists, the Guardian reported.

According to the report, when workers used content moderation software to police inappropriate material and ban administrators from Facebook groups, their profiles appeared as a notification and were viewable by the remaining admins.

Of those exposed, approximately 40 worked in the company’s counter-terrorism unit in Dublin, which employs contractors to monitor Facebook accounts for ties to organizations (like ISIS, Hamas, and the Kurdistan Workers Party) designated by the U.S. State Department as terrorist groups.

Facebook determined that the profiles of six of those 40 were “high-priority” victims of the breach, and were likely viewed by potential terrorists. One of those six, an Iraqi-born Irish citizen, fled the country and went into hiding after the breach.

The bug was discovered last November.