Facebook recommends patients with a psychiatrist's number on phone friend one another—outing them to each other. 

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why it is the time to leave WhatsApp for services such as signal
FB should, at best, use PII like this to train a recommender on more innocuous features, not as basis for recs directly.
But that wouldn't stop FB from outing a shrink's patients to one another. You can't get one burner per patient. https://twitter.com/Trojan7Sec/status/770972016950276097 …
Worst, Facebook's privacy insensitivity with phone metadata compromises WhatsApp & Two-Factor-Auth; but both are is essential for security.
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