Facebook bug temporarily unblocked people from 800,000+ block lists

If you block someone on Facebook, you probably want them to… you know, stay blocked. At least until you say otherwise.

Facebook has just disclosed that around 800,000 users were impacted by a bug that silently unblocked “some” people they had blocked.

The bug was live from May 29 until June 5, the company says.

Worth noting: The bug didn’t go so far as to make the would-be blocked individual your friend (even if they were your friend prior to the block), so anything an affected individual might’ve posted to a friends-only audience should have remained private. It would, however, allow a blocked user to do things like contact you on Messenger, or try to re-add you as a friend.

While Facebook isn’t saying much about what caused the bug, they’re sending out a notification (pictured above) to anyone they believe was affected.

Update — Facebook has shared some more details about the cause of the bug with TechCrunch’s Josh Constine via Twitter:

Hey Josh, it’s always hard to find the right level of technical detail to put in a blog post like this. More context on what caused the bug: most visible user data on FB is stored in pairs called “associations,” which control what posts people see and the actions they can take.

— Facebook (@facebook) July 2, 2018

A bug mistakenly deleted some of these associations across Facebook and Messenger, which caused blocks to be lost.

— Facebook (@facebook) July 2, 2018

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