https://motherboard.vice.com/en_us/article/3kjzvk/facebook-cambridge-analytica-not-a-data-breach

On Saturday, an investigation by The New York Times, the Guardian, and its sister publication The Observer revealed that the data analytics firm that helped the Donald Trump presidential campaign had harvested the Facebook data of more than 50 million people in an effort to profile users and eventually target them with political ads.

In 2014, a researcher collected the data through an app that asked users to take a personality test for academic research purposes. Around 270,000 people agreed to have their data collected through the test, which its creator, Aleksandr Kogan, defined as “a very standard vanilla Facebook app.” But thanks to Facebook’s terms of service and its API at the time, the app was also able to collect data of their friends. This gave the researcher, who later handed the data to Cambridge Analytica, the raw information of more than 50 million people, according to the reports, which were largely based on the account of a former Cambridge Analytica data scientist.