Afaik WhatsApp (on Android at least) requires you giving access to your contacts. So roughly speaking a huge chunk, probably the majority, of smartphone users s

Afaik WhatsApp (on Android at least) requires you giving access to your contacts. So roughly speaking a huge chunk, probably the majority, of smartphone users shared their contact list to at least one company, which strictly speaking might not even be legal in many cases. After all that's how WhatsApp populates its contact list, it looks which users have each other's phone numbers. That way it doesn't need a user login and friend/contact requests, but in return you give up your privacy.