When creating an account with Facebook, or any other social media site for that matter, you agree to Terms and Services or some other document. This document is a Contract of Adhesion, which means that the company has all of the bargaining power. As someone joining the site, you do not have any power to change or negotiate that document. You have the option to agree and join or decline and not join.
Most people tend to blindly accept without reading or understanding about the terms of their agreement. From this point on, the website begins to data mine. Every move made by each user is tracked and used as a data point to build a profile about you. This profile is a combination of what you post, tracking malware that knows what you look at or search, and sometimes even other things you have on your device such as your location or other websites. Through the third-party doctrine, the website is then allowed to share the profile of you that they have built with third-parties because by signing the agreement to join you waived any claim to privacy. This is Facebook's real product. They are not profitable simply from people interacting with each other. They make money by tracking those interactions and selling a profile of each person to other companies that use that information to for behavioral/targeted marketing. This is why we see advertisements for Oreo's after we talk about cookies or Nike advertisements when we post a picture from a sporting event.
For example, we can search the internet to see what the world knows about us. This search would be a lot more in-depth for a company that is entirely focused on doing this for profit, but it is an interesting exercise nonetheless. I was able to find my Instagram and Facebook accounts. We can build a profile about me based on the posts, pictures, comments, and posts that I am tagged in. I am not very active on either recently. Looking at Instagram, it is clear that I visited Penn State recently and am from Philadelphia. I like to post pictures with friends and there is the occasional karate video when you get farther down the page. On my Facebook search, you can find mostly pictures from when I was about 13. My Facebook posts and tags are almost entirely family-oriented. There is a karate trophy and an ex-girlfriend in my related photos as well. However, with a common name, you find a lot of other people along with yourself who tend to be more famous. When searching variations of my name (Tom, Tommy, Thomas), I find a character Jake Gyllenhaal played in a movie called
Brothers, a football player, and an author. Despite these other people, a third-party is more than capable of finding information about you especially with the help of social media companies to build a profile about you that they can use for behavioral marketing.
