[I_am_tiberius]

This one: If you don't use Whatsapp but a friend of yours does, he has to give Whatsapp access to his address book which includes your name as well (although you don't use Whatsapp). So the question is: Does Facebook/Whatsapp have information about such passive users (e.g. the name or phone number)?

[unfunco]

This is already known, yes, and they're called shadow profiles.

[I_am_tiberius]

Ok, good to know. But then I would like to know if these show (Whatsapp) profiles are used to match with existing Facebook profiles (based on phone number or name).

[lozenge]

The European Commission has fined Facebook €110 million for providing incorrect or misleading information during the Commission's 2014 investigation under the EU Merger Regulation of Facebook's acquisition of WhatsApp... When Facebook notified the acquisition of WhatsApp in 2014, it informed the Commission that it would be unable to establish reliable automated matching between Facebook users' accounts and WhatsApp users' accounts. It stated this both in the notification form and in a reply to a request of information from the Commission. However, in August 2016, WhatsApp announced updates to its terms of service and privacy policy, including the possibility of linking WhatsApp users' phone numbers with Facebook users' identities.

Facebook using the phone number they requested "for security purposes" to improve ad targeting and let people identify you from your phone number: https://www.forbes.com/sites/leemathews/2019/03/04/facebook-...

[I_am_tiberius]

Thanks for the detailed information. However, this seems to refer to a match between your own whatsapp number and your own facebook account. What I find even more interesting is that the entire address book can be matched, also if most of your address book contact don't have a whatsapp account but a facebook account!