SAN FRANCISCO — Do you know who can see what you are posting on Facebook, including your photos, birthday and personal cellphone number?
Chances are that you don't.
Facebook is worried that you will start sharing less — or maybe even move to more anonymous services — unless it helps you better manage your private information. So it plans to give a privacy checkup to every one of its 1.28 billion users worldwide.
Facebook will also change how it treats new users by initially setting their posts to be seen only by friends. Previously, those posts were accessible to anyone.
And it will explain to both current and new users that setting their privacy to "public" means that anyone can see their photos and posts.
The change in default settings and the person-by-person review is a sharp reversal for Facebook, whose privacy settings are famously complicated. Some users may be shocked when they see just how widely their personal information has been shared.
For most of its 10-year history, Facebook has pushed and sometimes forced its users to share more information more publicly, drawing fire from customers, regulators and privacy advocates. That helped make Facebook the world's largest social network and an advertising behemoth.
But the company recently concluded that its growth depended on customers' feeling more confident that they were sharing intimate details of their lives with only the right people.
"What we really want is to enable people to share what they want," said Mark Zuckerberg, Facebook's co-founder.
And more sharing means more growth and more opportunities to place ads for Facebook.