In a startling revelation about the 2016 U.S. election, it’s been revealed that a voter-profiling company named Cambridge Analytica harvested the data of more than 50 million Facebook users, without their permission, in efforts to sway voters to support President Donald Trump.

Cambridge Analytica was founded by billionaire Robert Mercer. Trump’s former adviser Steve Bannon of Breitbart News was one of the company’s key strategists.

The Facebook data was first obtained by a Cambridge University academic named Aleksandr Kogan, whose company Global Science Research built an app that paid Facebook users to take a personality test and agree to have their data collected. The app also collected the data of these users’ friends, meaning it actually collected data from tens of millions of users without their knowledge.

Cambridge Analytica then bought this data in order to turn a voter-profiling company into a powerful psychological tool, which began launching targeted political ads aimed at carrying out Robert Mercer’s far-right political agenda. This is whistleblower Christopher Wylie, who worked with Aleksandr Kogan to obtain the data from Facebook.

Christopher Wylie: “It was a grossly unethical experiment, because you are playing with an entire country, the psychology of an entire country, without their consent or awareness. And not only are you like playing with the psychology of an entire nation, you’re playing with the psychology of an entire nation in the context of the democratic process.”

The London Observer, The Guardian and The New York Times all helped break the story.

The revelations of the massive data breach and its role in the 2016 election has caused widespread backlash from both U.S. and British lawmakers, who are now calling on Facebook CEO Mark Zuckerberg to testify. This firestorm comes after Facebook has already faced massive backlash over how the platform was used to spread Russian propaganda ahead of the election.