https://www.reuters.com/article/us-facebook-cambridge-analytica-congress/u-s-lawmakers-formally-ask-facebook-ceo-to-testify-on-user-data-idUSKBN1GZ25A >U.S. lawmakers on Friday formally asked Facebook Inc's Mark Zuckerberg to explain at a Washington hearing how 50 million users' data got into the hands of political consultancy Cambridge Analytica.