[gizmogwai]

That's more subtle, as individual anonymized data point can not identify an individual, but a linked set of those can, with a very high percentage of confidence. Facebook can always play the card that each data point are anonymous, hence not part of your data, and keep everything.

[stavrianos]

Exactly this. Assuming that shadow-profiles are derived on-demand, the only way to "delete" one would be to delete the datapoints it's built from.

We know that facebook can use contact info to identify clusters, right? Suppose that I don't have facebook, but a bunch of my friends do, and facebook has all their contacts' phone numbers. They can infer the circle of friends of "whoever owns phone number X" using just this info. This is probably not the extent of a shadow-profile, but I think it's a plausible stab at the underlying mechanics (repeat again with email, with browser fingerprint, etc).

In order to "delete" my phone-shadow-profile, facebook needs to remove my phone number from their internal copies of my friend's contact lists. They also need to keep a copy of my number in a "do not shadow" list, or else they'll just add me back in next time they scrape my friends' contacts. Armed with a such a do-not-shadow list, there's no need to actually do the deletion, rather than simply marking the deletion.

So, assuming my speculations of the nature of shadow-profiles are about right, the only way to really avoid facebook having one is to register your fingerprints with them, so they can tell which parts of their data are you, in order to know not to use that data to draw inferences about you.

That, or give up on drawing inferences between disparate data-sources at all.

[mic47]

> In order to "delete" my phone-shadow-profile, facebook needs to remove my phone number from their internal copies of my friend's contact lists.

This is (potentially) not viable. Your friend's contact list is not your data, it's their data (about you) and they store it on FB servers. Right now it's probably used only for ranking and friend suggestion, so what you suggest would work. But if FB would decide that say messenger should work also as contact sync app (it already allows you to send SMS to people in your contact list), this would cause that your contact could not be synced, and really break user experience, as you would be able to delete your phone number from your friend's phone books.

More philosophical question: if you should be able to do that [delete your phone number from your friend's phone book on FB], should you be able to do that also from google contact sync server? From gmail? From your friends phone? Or from your friends physical (manually written) phone book? Where to draw a line, or how to approach this?