This is basically an off-shoot of any web-phishing scam, only instead of using the 'old' WoW login page or any type of 'WoLTK' phish, you use the newest feature of the Armory.
If you go to the Armory under either your own character, or a search for a guild, you will see some new options under the Guild tab. They are:
"Bank Contents"
or
"Bank Log"
Either of which requires you to log in to view it's contents.
If someone could come up with some phishing site, with the cooresponding .php code, they could come up with some scam, ranging from:
"OMG USING THE ARMORY PAGE YOU CAN STEAL ITEMS FROM ANYONE'S GUILD BANK"
and so on.
I am not fluent in .php code, otherwise I would have written the phishing site for myself, and shared it. But I can't, so I'm leaving it up to others.
I'm pretty sure this hasn't been covered here before, so I'm posting it here.
Good luck to all you coders.