[Uchikoma]

One has to ask, why don't they upload hashes? This would be sufficient to check for friends (email,telephone).

Why do they upload real data? Do they sell it? What happens when they go bankrupt?

[mdonahoe]

It's slightly more work, and devs are lazy?

Hashing doesn't really solve the entire problem, though it does prevent the service from getting addresses it doesn't already know. Allowing an app to see your contact list is an act of faith.

Maybe bloom filters can save us? :)