Databrokers enable this - take a look at something like Acxiom's developer APIs.[1] You'll find that they have some quite interesting stuff, like whether someon

Databrokers enable this - take a look at something like Acxiom's developer APIs.[1] You'll find that they have some quite interesting stuff, like whether someone's interested in gambling.[2] Facebook partners with these folks (as do many others) to enable them to build this aggregated database. Interestingly, you can log in and see your own profile there. I did that a few years ago, and introduced subtle errors into it (e.g. I changed my car to a different brand of car, and the "extended warranty services" robocalls around a year later started calling about my nonexistent vehicle). [1] https://developer.myacxiom.com/code/api/data-bundles/main https://developer.myacxiom.com/code/api/data-bundles/main [2] https://developer.myacxiom.com/code/api/data-bundles/bundle/gambling https://developer.myacxiom.com/code/api/data-bundles/bundle/...