Facebook said the bug was active for 12 days between September 13th and September 25th, during which time third-party apps that had access to a user’s photo gallery were able to also access photos that were not meant to be public:
In this case, the bug potentially gave developers access to other photos, such as those shared on Marketplace or Facebook Stories.
Facebook has created a help page that you can access at this link, to see whether you’re one of the 6.8 million people impacted by the bug.
You’ll see an image like the one above if your private photos were not accessed by any of your photo apps that you may have installed on your phone. Otherwise, a list of culprits will appear, and you may want to clean up the collection of private photos you uploaded to Facebook, in case you’re worried this might happen again.
Original article