http://www.washingtonpost.com/blogs/the-switch/wp/2018/03/22/why-facebook-users-data-obtained-by-cambridge-analytica-has-likely-spun-far-out-of-reach/

The data on millions of Facebook users that a firm wrongfully swiped from the social network probably has spread to other groups, databases and the dark Web, experts said, making Facebook’s pledge to safeguard its users’ privacy hard to enforce.

Facebook chief executive Mark Zuckerberg said Wednesday that the company will notify users whose data may have been taken by Cambridge Analytica, a political marketing firm that worked for the Trump campaign. Cambridge Analytica obtained the data of an estimated 50 million users in 2014 and 2015 under false pretenses, breaking Facebook’s rules. Zuckerberg said that Facebook, the world’s biggest social network, has taken steps to ensure that data on millions of its users does not get into the wrong hands.