So, I'm checking the #FacebookLeak, some people in there doesn't even have a FB account. But it turns out they have a WhatsApp one. In the leaked data WhatsApp users' ID seem to start with 1000. It also includes gender, which is not something one declares when registering on WhatsApp.
Remember that the leak is supposed to be from 2019. That tell us that, 2 years ago, #Facebook was already linking whatsapp data inside Facebook, even when you don't have a FB account, and pushing data from facebook to your #WhatsApp data, like the gender. Two ways binding.
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