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Comment by arrty88 | Hacker News Reader

How? Is it public on your profile page? Have you ever used facebook apps or oauth/single sign on?

Nope, contact info is hidden. Never authed with another app or service. The idea of super cookies doesn't play either, I only use Facebook in a separate browser that doesn't get used for anything else, and these days it only gets used in Firefox using the Facebook container. I've always treated Facebook like the plague and never let it come close to my normal activities. I went to great lengths to not let them figure out who I was, other than the graph info they have on my friends.

You were probably tracked via IP address. Even without a static IP address, it probably doesn't change that much. With so many Facebook "like" icons everywhere, it doesn't really matter what browser you use, or if you are logged in or not.

Data brokers sell contact lists that advertisers upload to facebook for targeting. Maybe this has changed, but last I checked, you could upload lists of emails, phone numbers, and/or facebook IDs.

All you need is for one of those identifiers (email, phone number, facebook ID) to show up on a list somewhere. Since you say your email is unique and only used for Facebook, it's unlikely that was used for targeting. Your phone number could be acquired from somebody else syncing their contact list to some app or service. Your facebook ID could be acquired from you authenticating to an app or service via facebook, or it could be scraped from public group pages.

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