The so-called Open Graph API included not only a user's name, birthdate, politics, and religion—private direct messages could be requested too—but also his or her friends' data.

Meta explained that a major use case for the API was a feature that allowed developers to privately reply in Facebook Groups. For example, a small business that wanted to send a single message to ...

Facebook uses a different API now. But before 2014, Graph API v1.0, as it was called, allowed those developers to collect a stunning amount of information about you — and your friends.