[techmagus]

Exactly. People who save your details in their Address Book and click the "Sync your Contacts" when an app suggests it, are the loophole in privacy and security.

The only way is to have a separate set of email, phone numbers, for those family and friends who doesn't care about privacy and security, that way it is easy to dispose those information later.

Beyond that … if we truly want to avoid it … the only course of action is to not give them anything at all. Not a single email, not a single phone number, not even our home addresses.

[wyclif]

That is exactly how I deal with it. I use a throwaway webmail address and a Google Voice number. No way they're getting my real email or phone number that I use for work and clients.

[InternetUser]

You're not avoiding having a shadow account created about you though, once I've upload my contact list and you're right there, Jim Wyclif, with your real phone number, and I've also tagged you in a photo we took together last year. And then there are all the other people who have your real phone number and who have been on Facebook, Messgenger, Instagram, or WhatsApp since they saved the number. And then there's even relatives and former classmates and co-workers who've looked up your name and typed in your town, school, and/or former company to find you. When I use Facebook, it still recommends former classmates and acquaintances who I literally looked up once ever. (As a side-note, Snapchat does the same type of things; people I've worked for in the past, as a tutor, are recommended to me on the "Add Friends" page.)

[dheera]

I wonder if there would be a market for a cloud-synced, client-side-encrypted address book app for say $1/month.