For example facebook can collect your data even if you are not using any of their services
Few people in each group will share a picture that youre in, on their Instagram story. Since youre the only person without an account you stand out. Theres only one person exclusively in these group photos. Theres only one person exclusively in these peoples contact lists.And everything is legal as far as i know i dont know much to be honest,and they can even get your name phone number,email photo and other things and well they have too much processing power so i have no idea what they can do
Prefered solution is apple and google not letting access to all the contacts like they doing for the photos, google has itroduced scoped storage and apple has something called as limited access we need that for the contact also .
An attempt to make fake contacts to do data poisoning, to make it hard for the abuse data if abusing like this