Cambridge Analytica claims to use data 'to change audience behaviour'. But now a whistleblower, Christopher Wylie, has come forward to expose the company's practices. Wylie describes how its CEO, Alexander Nix, attracted support from the then Breitbart editor, Steve Bannon, and investment from the billionaire Robert Mercer before obtaining help from the Cambridge professor Aleksandr Kogan to harvest tens of millions of Facebook profiles

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