A political consulting firm obtained personal data from over 50 million Facebook users without their permission, according to a Facebook announcement on March 16. Data obtained from the leak was used to attempt to sway the results of the 2016 presidential election.

The consulting firm, Cambridge Analytica, had been hired by President Donald Trump’s 2016 election campaign to identify the personalities and behaviors of American voters. According to The Observer, Cambridge Analytica was collecting data from users through a personality survey app called thisisyourdigitallife that also managed to take private information from both the user’s profile and their friends’ profiles. The firm then used the data to “predict and influence choices at the ballot box.”

The quiz app was designed in 2014 by Aleksandr Kogan, a Russian-American researcher at Cambridge University’s Psychometrics Centre. Kogan had been hired by Christopher Wylie, a data analyst and one of the founders of Cambridge Analytica, and Alexander Nix, the chief executive of Cambridge Analytica.

Wylie, who left the firm in 2014, came forward as a whistleblower and spoke out about Cambridge Analytica to The New York Times and The Observer.

Cambridge Analytica has been suspended by Facebook for violating standards and practices for the social media site. Strategic Communication Laboratories, the parent company of Cambridge Analytica, was also suspended from Facebook for violating its rules for data collection and retention. Wylie’s lawyer, Tamsin Allen, said Wylie has offered to help Facebook recover the data obtained during the leak, but Facebook said on March 18 that Wylie is refusing to cooperate until the suspension on his Facebook account is lifted.

Paul Grewal, vice president and deputy general counsel for Facebook, told The New York Times that no passwords or other sensitive data were leaked during the breach but that Cambridge Analytica’s actions were “a serious abuse of our rules.”

Facebook stocks have dropped 7 percent since the announcement of the misuse of user data, one of the worst drops for the company’s shares in four years. The net worth of Mark Zuckerberg, the founder and CEO of Facebook, has also dropped — his net worth was roughly $69.5 billion at noon on March 19, in comparison to nearly $75 billion on March 16.

Lawmakers are calling on Zuckerberg to testify about the data leak and how his company failed to crack down on the data mining operation.

“They say ‘trust us,’ but Mark Zuckerberg needs to testify before the Senate Judiciary Committee about what Facebook knew about misusing data from 50 million Americans in order to target political advertising and manipulate voters,” Sen. Amy Klobuchar, D–Minn., said in a statement on the breach.