But...all of your contacts stopped talking to one number, and started talking to the new burner number.

They know it's you.

Every single one of your friends will add a contact to their phone, with 1: The new phone number, 2: Your real life name. They'll then go and share that contact list with a dozen different apps, including Facebook and Whatsapp. Some of them will add your email address, birthday, and home address to that contact as well.

Information asymmetry is a motherfucker - and they have it all.

Facebook cannot know it, since it is another phone no. not used anywhere else. The point of using another SIM card in Android VM is that Whatsapp doesn't have access to your Facebook profile, your web activity, your real phone no., real location, MAC address of your primary smartphone etc. Meanwhile you can use Signal/Telegram/iMessage to chat with your Whatsapp contacts.

> Facebook cannot know it, since it is another phone no. not used anywhere else.

They just compare the set of friends with whom you spoke using your original number and with whom this new number speaks now. Otherwise you are right.

Would they really do this? Lots of people have multiple phones anyways.

Yes. They really would do this.

They use a probability factor to identify similarity with other users. If the similarities match high, they internally identify it as a probable identical profile.

But for this to happen successfully, they would have to use the first profile that didn’t agree to new terms and compare it to new profile that did agree to new terms.

Btw, somewhere in Facebook land they are trying to workaround this hack. Which means FTC should be all over this.

It takes something like calling 3 phone numbers to uniquely identify the owner of a phone number.

Connecting to several of your old friends is more than enough to identify someone with an incredibly high level of confidence.

(Example list of people: someone at your job or a friend, another friend, your mother.)

Possibly, but it's still better than using Whatsapp as before.

It's a half measure technical solution to a political problem.

Obscure, please, in all seriousness - but fund the EFF, and vote for people who support data privacy vocally.

I think the point is that the burner number only gives you a weak pseudonymity. Your contacts and your communication profile (how often are you talking with whom) is still visible and it seems not unlikely that it can be matched to the one in Facebook purely by that.