Like many others, PI were alarmed at recent reports that Facebook have been making mobile phone numbers (which users believed to be) provided for the express purpose of "two-factor authentication" (2FA) both searchable, and a target for advertising by default.
One of the myriad ways Facebook displays targeted adverts to users is through so-called "Custom Audiences". These "custom audiences" are lists of contact details, including phone numbers and email addresses, uploaded by advertisers.…