Myanmar’s Military Said to Be Behind Facebook Campaign That Fueled Genocide - The New York Times:

While Facebook took down the official accounts of senior Myanmar military leaders in August, the breadth and details of the propaganda campaign — which was hidden behind fake names and sham accounts — went undetected. The campaign, described by five people who asked for anonymity because they feared for their safety, included hundreds of military personnel who created troll accounts and news and celebrity pages on Facebook and then flooded them with incendiary comments and posts timed for peak viewership.

Perhaps it “went undetected” because this sort of malign usage is indistinguishable from Facebook’s core business model.