Let me address the things mentioned in the article:
No data is ever sent or received to or from our servers in plain text. Due to a bug in our third-party network library the certificates were not being verified so a self signed certificate could decrypt the data. This issue has been addressed in an update waiting review at Apple. Users' passwords are hashed before we store them in our databases (pbkdf2, salt, multiple iterations).
Our user's address books are not stored on our servers and only used temporarily to help us find your friends. It was a mistake to not hash the contents of the address book before sending to our servers and we are currently changing the client application so it hashes the address book contents before sending to our servers.
Sensitive user data was exposed in certain endpoints (although only accessible for authenticated users). We have already addressed this issue in a server deployment and the hotfix is live now.
We are currently wading through inboxes looking for Kyle’s outreach. It looks like it may not have reached the core server developers. Please contact me personally at jokull@plainvanilla.is if you have questions.
Finally I want to thank Kyle Richter for working out our security holes, small and large. We’re currently reviewing our endpoints and codebase to further harden security and ensure the privacy of our users.