Facebook Messenger – Discoverability of Phone-Number-Only Messenger Users by Full Facebook Users

I read a question on Information Security about how Facebook could know recommendations of friends by just a phone number.

The answer to that question explicitly details that the more probable scenario is one in which the friends of the phone contact shared the information to Facebook.

So let's start there. Let's assume a phone number is in a contact list "123-4567"

At this point, before a friend syncs to Facebook. All this is a number, not a name, not an address.

You can state here that Facebook holds phone numbers (because Facebook users allow them to) to assist with the Suggested Friends / People you may know feature.

With you interacting with Facebook in anyway

https://www.facebook.com/legal/terms

Special Provisions Applicable to Users Outside the United States

We strive to create a global community with consistent standards for everyone, but we also strive to respect local laws. The following provisions apply to users and non-users who interact with Facebook outside the United States:

You consent to having your personal data transferred to and processed in the United States.

If you are located in a country embargoed by the United States, or are on the U.S. Treasury Department's list of Specially Designated Nationals you will not engage in commercial activities on Facebook (such as advertising or payments) or operate a Platform application or website. You will not use Facebook if you are prohibited from receiving products, services, or software originating from the United States.

Certain specific terms that apply only for German users are available here.

Definitions

By "Facebook" we mean the features and services we make available, including through (a) our website at www.facebook.com and any other Facebook branded or co-branded websites (including sub-domains, international versions, widgets, and mobile versions); (b) our Platform; (c) social plugins such as the Like button, the Share button and other similar offerings and (d) other media, software (such as a toolbar), devices, or networks now existing or later developed. By "Platform" we mean a set of APIs and services (such as content) that enable others, including application developers and website operators, to retrieve data from Facebook or provide data to us. By "information" we mean facts and other information about you, including actions taken by users and non-users who interact with Facebook. By "content" we mean anything you or other users post on Facebook that would not be included in the definition of information. By "data" or "user data" or "user's data" we mean any data, including a user's content or information that you or third parties can retrieve from Facebook or provide to Facebook through Platform. By "post" we mean post on Facebook or otherwise make available by using Facebook. By "use" we mean use, run, copy, publicly perform or display, distribute, modify, translate, and create derivative works of. By "active registered user" we mean a user who has logged into Facebook at least once in the previous 30 days. By "application" we mean any application or website that uses or accesses Platform, as well as anything else that receives or has received data from us. If you no longer access Platform but have not deleted all data from us, the term application will apply until you delete the data.

In terms of the registration specifically, since you never finished the process then the user you registered isn't validated. Why would Facebook store dirty data since 2006?

With actual requests of data use this form

https://www.facebook.com/help/contact/166828260073047

Facebook will recognise the number and tell you to either:

• "Log in with Facebook" (thus connecting your full account)
• or "Continue signing up" (which will keep your new Messenger identity separate, and you will go on to enter a first name, last name, and optionally a photo).

If you do this separate phone number sign up, and you search for your own name in the contact search screen, you may be able to find what looks like a full Facebook profile of yourself. Nope, they did not reactivate your full account. They actually seem to create a new Facebook account with your name, phone number, and profile photo all publicly visible - this is presumably their chosen way make you discoverable to people with full Facebook accounts.

Source: Messenger for iOS (UK)