https://www.cnbc.com/2018/06/07/facebook-bug-made-private-posts-of-up-to-14-million-users-public.html

About 14 million Facebook users who thought they were posting a message just to friends or smaller groups may have actually been sharing it widely with the general public due to a software bug, the company said Thursday.

A Facebook user's post typically defaults to a preselected privacy setting. However, a bug that was active from May 18 to May 27 changed posts to automatically be public.