No, no, it wasn't Seed of Corruption this time. It happened with the new Druid spell Typhoon. Specifically Typhoon Rank 5. It's already been hotfixed, so don't bother trying it now- you missed out. If you want to see exactly what people were doing with this spell, just check out the video above.
I had a chance to experience a little of this firsthand, and it was impressive, to say the least. A Moonkin rolling up to an enemy faction's town and laying waste is just hilarious to see, though not so much after the tenth time. Remember, this thing didn't even trigger the Global Cooldown. Druids were running around with macros that cast this spell ten or twenty times simultaneously. Nothing could even hope to survive, especially when you got a bunch of them together. Five or six Moonkin in Naxx-25 was just absurd.
If you want to see more of the bug, the tipster that supplied the above video has a whole bunch of them. Balance Druids, I hope as many of you got in on this as possible. Everyone gets a turn to be horribly, hideously overpowered. That was yours.
[ Thanks, Bular! ]