They need to enforce their own TOS as well as follow them in the first place. "The one rule that Cambridge professor Aleksandr Kogan violated, according to Facebook, was passing user data to third parties, including Cambridge Analytica. But even [CNN's] Facebook sources acknowledge that it is impossible for the company to completely monitor what developers and advertisers do with the data. "This is why it is so hard to trust Facebook when they say 'protecting people's information is at the heart of everything we do.' In fact, Facebook's business is providing people's information to outside parties whose ultimate goals are unknowable."