It is absolutely not possible to get account information, unless you specifically tell someone else your user/password INGAME and somehow a malicious addon catches it.
I've been writing WoW Addons for years now and I know the limits. Seriously, ask anybody who actually has a clue.
The worst you could ever do is create an infinite loop to crash a game, monitor chat or send mails whenever the user opens the mailbox without them noticing (albeit, only in Vanilla).
@OP:
You should post this on other servers (smaller ones) too, they might even need it more.