username of invitee exposed, in case the invitee is already a registered user

When inviting an already registered user by e-mail, the module exposes his username (stating "!email is already registered as !username" or similar).

I see a privacy risk in this chatty behavior, because it is possible for a Bully to find out the username of his victim just by providing his e-mail. The reason for having usernames is, to decouple the real identity (often losely bound to an e-mail address) from the virtual identity.

Would be nice to remove that message, or to add an option to enable it (which would be turned of by default).