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

Facebook’s advertising platform is riddled with loopholes that can help miscreants obtain private information on individual users, according to a recent study.

Personally identifiable information – such as someone's email address, full name, date of birth, and home address – are used with their likes and dislikes to slot them into categories for targeted adverts. That means advertisers can zero in on their products' ideal buyers, and, say, sling expensive pet food ads at rich dog owners. However, these systems can also be exploited by scumbags to slurp sensitive records.