Colour me chuffed.
I was correct in my suspicions, and whoever had managed to compromise my account had indeed stripped and deleted two of my level 70 characters. The last time I had logged on, I had three characters at level 70; a Horde Druid and Priest and an Alliance Warrior. On checking the Armoury, both the Priest and Warrior were missing, and the Druid was naked – which, as I'm sure any other Tauren player can attest, is rarely a good look.
Now, as much as I deplore it, I can understand the concept of hacking a person's account in order to sell their gear, then pass that money along via a Goldseller – that's simply business, but I don't understand why you would delete a character completely – while the first is an undeniably rotten thing to do to a person, it's generally something that can be recovered from, or (in the worst-case scenario) rebuilt. New gear can be acquired, gold can be earned once again, and if your guild happens to be chock-full of good folk like mine, you'll maybe get some help along the way.