A Facebook bug turned 14 million users posts into public posts over a 5 day period in May. CNN Money reported the bug was the result of an un-proclaimed Facebook test, and that Facebook then made all posts created by affected users into private posts. Without telling them. Because [Facebook].

Facebook announced the bug today and will be notifying affected users starting today.

“We recently found a bug that automatically suggested posting publicly when some people were creating their Facebook posts,” Erin Egan, Facebook’s chief privacy officer, said in a statement. “We have fixed this issue and starting today we are letting everyone affected know and asking them to review any posts they made during that time. To be clear, this bug did not impact anything people had posted before — and they could still choose their audience just as they always have.”

Facebook Bug Affects 14 Million Users

Here’s how it worked: Facebook was testing some new unannounced feature, or as I like to call it, experimenting on its users, As an unintended byproduct of this test, the members being experimented on had their default post status set to “public” from May 18th through May 22nd. Usually, your message status is whatever you chose last. Any user who noticed the “public” status and changed it to some form of private status would have posted as intended. Everyone else made their posts public.

Facebook noticed the problem and spent another five days making all posts by the affected users private—again, without telling us until today—regardless of their original intent (because Facebook wouldn’t know their original intent). Starting Thursday (today). affected users will get a message from Facebook asking them to review the affected posts.

And, get this, Facebook called today’s announcement—despite the many days that have elapsed since discovering and then correcting the problem—part of its new effort to be proactive and transparent.

Pretty cool, right?