https://www.theregister.co.uk/2018/04/12/uh_oh_as_zuck_gets_grilled_in_congress_boffins_find_new_ways_to_exploit_facebook_users_with_targeted_ads/

Facebook’s advertising platform is riddled with loopholes that allows people to gain private information about its individual users, according to a recent study.

Personally identifiable information such as a person’s email, full name, date of birth, and address, and their likes and dislikes are used to create categories for targeted adverts. It’s a useful tool for advertisers looking to expand their audience on social media, but it can also be exploited by adversaries to steal sensitive data.