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Time to get serious with E2E encrypted messaging
(techcrunch.com)
This is a most excellent place for technology news and articles.
You can enable a registration lock, where anyone with your number would have to enter a pin to register an account with it. However, it removes itself if you don't log in for a while.
Yep, that's what I was thinking of. I guess just set a reminder to login every now and then (if you don't use regularly).