Exploiting Facebook data to influence voters? That's a feature, not a bug, of the social network

With each comment, like and share, users provide Facebook with a deeply personal window into their lives.

The result of that voluntary behavior? Advertisers looking to finely target their pitches can glean someone's hobbies, what they like to eat and even what makes them happy or sad - propelling Facebook's ad revenue to $40 billion last year.

This trove of rich information is now at the center of a rapidly growing controversy involving one of President Trump's campaign consultants, Cambridge Analytica, which reportedly took the advertising playbook and exploited it in a bid to influence swing voters.

Former employees accuse the firm, owned by the conservative billionaire Robert Mercer and previously headed by Trump's former chief strategist Steve Bannon, of taking advantage of ill-gotten data belonging to millions of unwitting