Update on March 17, 2018, 9:50 AM: The claim that this is a data breach is completely false. Aleksandr Kogan requested and gained access to information from users who chose to sign up to his app, and everyone involved gave their consent. People knowingly provided their information, no systems were infiltrated, and no passwords or sensitive pieces of information were stolen or hacked.

Originally published on March 16, 2018:
We are suspending Strategic Communication Laboratories (SCL), including their political data analytics firm, Cambridge Analytica, from Facebook. Given the public prominence of this organization, we want to take a moment to explain how we came to this decision and why.
[...]
In 2015, we learned that a psychology professor at the University of Cambridge named Dr. Aleksandr Kogan lied to us and violated our Platform Policies by passing data from an app that was using Facebook Login to SCL/Cambridge Analytica, a firm that does political, government and military work around the globe. He also passed that data to Christopher Wylie of Eunoia Technologies, Inc.

Like all app developers, Kogan requested and gained access to information from people after they chose to download his app. His app, "thisisyourdigitallife," offered a personality prediction, and billed itself on Facebook as "a research app used by psychologists." Approximately 270,000 people downloaded the app. In so doing, they gave their consent for Kogan to access information such as the city they set on their profile, or content they had liked, as well as more limited information about friends who had their privacy settings set to allow it.

Although Kogan gained access to this information in a legitimate way and through the proper channels that governed all developers on Facebook at that time, he did not subsequently abide by our rules. By passing information on to a third party, including SCL/Cambridge Analytica and Christopher Wylie of Eunoia Technologies, he violated our platform policies.

whose terms of use? Who owns the data?

Diversity is the key to economic and political evolution.