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The reason that Facebook changed their policy to disallow targeting to a very small audience is because of this paper http://repository.cmu.edu/cgi/viewcontent.

The reason that Facebook changed their policy to disallow targeting to a very small audience is because of this paper http://repository.cmu.edu/cgi/viewcontent.cgi?article=1066&context=jpc http://repository.cmu.edu/cgi/viewcontent.cgi?article=1066&c... It studies the same problem as the author here exploited, but goes a lot farther to try and infer things about the targeted individual from the analytics that FB provides to the advertiser. The paper won the Privacy Enhancing Technologies award. That was back in 2010. If the author succeeded anyway, it seems that Facebook was careless in their implementation of the fix.

RexRollman 12y ago
Or they don't really care.
petercooper 12y ago
In this case they used Custom Audience Targeting which is different to what's used in the paper. CAT is advertising based on a list of personally identifiable information about your "targets" that you supply, which can include user IDs, phone numbers, e-mail addresses, etc. I can't confirm but suspect no limit is required for this since you already have their personal data. As an aside, an interesting use of this system I've seen in the Internet marketing world is to buy e-mail or phone number lists from list vendors and use them to create custom audiences in Facebook. You can't e-mail them because that's spam and you'll be busted very quickly, but using them as fodder for custom audiences on platforms like Facebook is a way of laundering the info, in a sense. (I've not tried it myself but thought the idea was clever.)