After hearing this from a few people, I ****ed around with Netlimiter and here are some interesting results if you limit WoW's download rate to 0.
  • All npcs/mobs disappear, you cannot perform any actions apart from move, you cannot zone into instances, you cannot drown.
  • Other players will still see you move and be able to kill you but your corpse will keep moving, on your screen you are still alive.
  • If you have been killed you will die at the spot where you changed the download rate back to normal, not where they killed you, hence "corpse walking".
  • NPCs/Computer mobs cannot harm you.
  • You get disconnected after 3-4minutes, but if you reset WoW's download rate back to normal you will not.
I would define this as a exploit/glitch, since you can move through trash mobs in instances/places without being harmed. Would be pretty hard to ban unless Blizzard detects the programs and there are a wide variety which limit net speed.
Andrew     
Definately an exploit if you ask me