Facebook is not your friend.

In 2011, Max Schrems, a 24-year-old Austrian law student, sued Facebook’s Dublin office for a complete record of his personal data. He received 1,222 pages of information covering three years of Facebook activity. But that wasn’t the biggest surprise.

What you don’t know they know.

Facebook’s report included deleted wall posts and messages, some with sensitive personal information, along with e-mail addresses he’d deleted and names he’d removed from his friends list. “It is very likely that no government or corporation has ever managed to gather such a huge amount of personal and often highly sensitive data,” wrote Schrems in his complaint. As of May, 2014, his action spurred more than 1,000,000 requests for Facebook data in Europe (not an option in the U.S.—can you guess why?).

Ignorance isn’t bliss.

Although you worry about the dangers of disclosing personal information on social media sites, you do it anyway (see: The bare necessities: food, water, and Facebook). “Meh,” you say, “I have nothing to hide.” Splendid, but you are not your profile. Databases can contain errors, and data compiled from disparate sources and differing contexts can lead the user of your data to misjudge your tastes, preferences, and character. Data brokers buy, compile, and sell a wealth of highly personal information about you, but there’s no way to find out what they have or if it’s correct.

A Consumer Reports (2012) cover story revealed how little we know about the enormous amounts of highly sensitive information that Facebook collects and distributes—quickly and widely—to third parties. The report highlighted many areas of concern regarding Facebook and personal privacy:

Some people are sharing too much. Projections suggest that 4.8 million people have used Facebook to say where they planned to go on a certain day (a potential tip-off for burglars) and that 4.7 million “Liked” a Facebook page about health conditions or treatments (details an insurer might use against you).
Some don’t use privacy controls. Almost 13 million users said they had never set, or didn’t know about, Facebook’s privacy tools. And 28% shared all, or almost all, of their wall posts with an audience wider than just their friends.
Facebook collects more data than you may imagine. Did you know that Facebook gets a report every time you visit a site with a Facebook “Like” button, even if you never click the button, are not a Facebook user, or are not logged in? Much of this activity occurs below your radar.
Your data is shared more widely than you may wish. Even if you have restricted your information to be seen by friends only, a friend who is using a Facebook app could allow your data to be transferred to a third party without your knowledge.
Facebook is “leaky.” Even when you don’t explicitly state facts about your life, data brokers “infer” more information because of social network analysis. These inferences have the potential to jeopardize your career, insurance coverage, creditworthiness, and relationships.

Your reputation is not their problem.

It’s yours, dude. Sure, Facebook offers many privacy controls, but good luck understanding them. Consumer Reports offers these tips to better control your social media information:

Think before you type. Even if you delete an account (which takes Facebook about a month), some info can remain in Facebook’s computers for up to 90 days.
Regularly check your exposure. Each month, check out how your page looks to others and review individual privacy settings if necessary.
Protect basic information. Set the audience for profile items, such as your town or employer. Resist the temptation to add people you don’t really know or don’t want to engage with. Sharing info with “friends of friends” could expose it to tens of thousands.
Know what you can’t protect. Your name and profile picture are public. To protect your identity, don’t use a photo, or use one that doesn’t show your face.
“UnPublic” your wall. Set the audience for all previous wall posts to just friends.
Turn off Tag Suggest. If you’d rather not have Facebook automatically recognize your face in photos, disable that feature in your privacy settings.
Block apps and sites that snoop. Unless you intercede, friends can share personal information about you with apps. To block that, use controls to limit the info apps can see.
Keep wall posts from friends. You don’t have to share every wall post with every friend. You can also keep certain people from viewing specific items in your profile.
When all else fails, deactivate. When you deactivate your account, Facebook retains your profile data, but the account is made temporarily inaccessible. Deleting an account makes it inaccessible to you forever.

Additional tips on how to maximize privacy settings on your Facebook profile are offered by the U.S. Army (2015).

Privacy has never been so public.

We value privacy, but fear privacy no longer exists—a 2014 survey by Pew Research Center found that 91% of American adults say consumers have lost control over how personal information is collected and used by companies. The good news? After Facebook triggered a backlash when it opted users into new sharing rules without their explicit consent, 86% of Internet users say they’ve now taken steps to remove or mask their digital footprints.