It's one guy playing 4 machines with a sick dual boxing setup, demo'd on
The original MMORPG Dual-Boxing and Multi-Boxing Site!. I've played against this guy in 5v5 several times over the course of a night, and it was most certainly frustrating as hell, but it's certainly not cheating. He's running multiple accounts, multiple machines, and a setup that lets him directly control all of them at once. It's not botting and not against the ToS. (And yes it is disgustingly frustrating to play against 4/5 elemental shaman without big CC on your team)