Facebook has 2.6 billion active monthly users across the world and knows a surprising amount about us---information we willingly volunteer.

It's not just basic details like name, age, and education: some are very personal and will make you want to check the Facebook privacy policy. Social networks are businesses. So what does this particular business know about you? How can you change your privacy settings on Facebook?

Facebook Knows Basic Information About You

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The line between your personal and online lives is immediately blurred. You surrender basic facts on sign up. You submit your name, email address, gender, and birthday. Facebook also needs to know who you're friends with---otherwise, there's little point. Through this, you can be linked to your family members and where you studied.

Facebook asks for your sexuality, current relationship status, political and religious views, location, and if you have your own website or blog. Using these, you're slotted into a demographic.

ABC1 is a key target, encompassing middle-class professionals with disposable finance. Fortunately for Facebook, nearly 75 percent of high-income earners are on the social network.

Snapchat is a huge rival to Facebook, but the latter still has serious sway with the traditional target age bracket, 18-34. Over 40 percent of Generation Z say they struggle with knowing which media to consume, so social media is vital to production companies, book publishers, and podcast services.

This is important because it means Facebook can command higher prices for advertising.

And because you're tagging friends' locations in status updates and photos, your ads can be personalised further to include advertisers in your locality. These can be generalized, but can be specific too---like how shops can track visitors using Wi-Fi.

Facebook Knows What You're Interested In

Nineteen-Eighty-Four George Orwell surveillance

Your profile documents subjects you like, including music, films, and books. Your timeline shows websites and articles you've shared. Facebook can tailor advertisements to better suit your "likes".

In a January 2015 study, intelligent machines assessed the "likes" of over 86,000 Facebook users to predict personalities, with surprisingly accurate results. The investigation examined agreeableness, conscientiousness, extraversion, neuroticism, and openness. Cambridge University's Dr David Stillwell told The Independent:

"The ability to judge personality is an essential component of social living, from day-to-day decisions to long-term plans such as whom to marry, trust, hire or elect as president... The results of such data analysis can be very useful in aiding people when making decisions."

Anything you post to your timeline or anyone else's is also recorded, as are Direct Messages. This data is sold on. Raw information is compiled to find trending topics, and is passed on to third-parties.

At least this data isn't personally-identifiable. A list of popular TV shows, for instance, will be shared with stations like ABC, CNN, and Fox, but those partners can't trace them back to individuals.

Facebook Knows What You Look Like

This is particularly creepy. However, what the technology enables you to do is cool.

how does social media facial recognition work

Facebook can suggest tags of you in friends' photos and vice versa. But far from simply telling what's a face, and what's, say, a close-up of a boiled egg, Facebook can distinguish you so well that it can automatically suggest tagging you in other people's albums.

The facial recognition project, DeepFace, compares two different images and locates the same person in each, regardless of lighting or angle. DeepFace works in a similar way to smartphone's Face ID, storing your visage as data. It detects distinctive patterns (cheek bones, chin, eyebrows), symmetry, and relative measurements. It then creates an abstract based on a nine-layer neural network, a series of interconnected nodes similar to the synapses of the brain). DeepFace can then recommend tags for similar patterns.

Facebook knows what you look like, with the same level of accuracy as the human mind (around 97 percent).

Fortunately, you can review your tags, and deselect unflattering images.

A Summary of What Facebook Knows About You

If you volunteer this information, i.e. either actively input data or simply share and like topics and articles, Facebook knows:

Your name; email address; gender; date of birth; who you're related to; who your friends are; which educational institutions you went to; sexual preference; relationship status; religious views; your job; where you live; if you have any political affiliations; the address of your own website or blog; your favorite music; which books you love; TV shows you enjoy; favorite films; your phone number; the contents of messages you post on your own timeline; messages other people post on your timeline; the contents of DMs; which websites you frequently visit; topics you regularly talk about; and what you look like.

This is in addition to any information the company gleans from third-parties, and brands under the Facebook umbrella like Instagram and WhatsApp. We don't know how Facebook's acquisition of Giphy will affect users either: more information may be collected, contrary to Facebook's statement that little will change.

And it doesn't matter if you don't have Facebook. Information is collected about non-users and shadow profiles are created.

How to Change Your Privacy Settings on Facebook

Review privacy settings on Facebook social media

It's easy to become complacent and give away a large part of your identity. Facebook is using your data to sell things. Most companies do.

So what can you do to protect your privacy on Facebook?

Click on the downward arrow to the top-right of your timeline. Then click on Settings & privacy > Settings. Select Privacy on the menu to the left, and toggle individual tabs. You can switch to Your Facebook Information and Timeline and tagging too. Alternatively, go on Settings & privacy > Privacy Checkup and review data on the service.

All of this can help keep your Facebook profile anonymous.

Concerns have also been expressed over Facebook listening to conversations via smartphones. Facebook has denied that it accesses your mic in this way, but some users remain skeptical. If you think your phone's listening in for targeted advertising, check your app permissions now.

Should You Delete Facebook?

You're probably looking for a more permanent solution, and the obvious one is deleting or deactivating your Facebook account. There's a big difference---the former completely gets rid of your account, while deactivation is a short-term way of distancing yourself from the platform.

But deletion is really about damage limitation. It won't affect those aforementioned shadow profiles, and some data still exists.

It's still a sound option, but before you take any of these steps, you should investigate what deactivation and deletion mean for your privacy.