The company said Thursday that a bug in its system caused it to publicly share the posts of 14 million people who thought they were making private updates. As a result, from May 18 to May 27, as many as 14 million users who intended posts to be available only to select individuals were, in fact, accessible to anyone on the Internet. Every Facebook user, though, has the ability to change these settings to post privately, to just friends, or to exclude certain people from seeing it.
"It will take some time to work through all the changes we need to make across the company", Zuckerberg said on the first day of hearings.
Facebook said it had reverted the audience settings to users' prior preference.
Posts are public by default for new accounts, but every Facebook user can limit who sees each post by using what the company calls an "audience selector". 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.
How did the bug impact Facebook posts?
The specific tool being tested was a "featured items" option on a user's profile that highlights photos and other content.
A message will prompt them to "Please Review Your Posts", while a link will direct the user to view a list of what they shared during the 10 days that the bug was active. These featured items are publicly visible, but Facebook inadvertently extended that setting to all new posts from those users.
It was unclear if users could have done anything to their settings to prevent being affected by the bug the company revealed on Thursday.
The news follows a recent furor over Facebook's sharing of user data with device makers, including China's Huawei. In the process of creating this feature, Facebook said it accidentally made the suggested audience for all new posts public.
Facebook has stated that these types of notifications will be used going forward to report privacy issues or breaches.
It's the latest in a series of revelations about Facebook's privacy lapses.