iCloud and iPhone Messages sync'd from unknown parties

My wife has a iPhone6 running IOS 9.3.1.

It has started syncing messages from unknown iCloud users.

We've turned off iCloud sync and all her contacts disappeared from the phone as expected.

- When we re-enabled it her original 70 or so were there.

When you start a new message to one of those recipients; there are now hundreds of unknown recipients appearing as you type the name.

- 15 "Dads"

- Multiples of unknown users and their emails.

We're concerned that the account has been hacked/hijacked by another user(s) and had previously been hacked by Chinese hackers.

Is this a new "feature" of iMessage?

Is this a 9.3.1 Bug?

Is the iCloud hacked?