This video shows the NoClip hack in action on live servers. While the game text is in Chinese, this hack was used on USA servers. It is a working game hack for live, official World of Warcraft servers. Many farmers use this hack in both China as well as in Korea and Russia to farm gold on USA and EU servers.
Video courtesy of RPG-Exploiters.com and UberGold.com. More information about this hack can be found in the VIP forums at rpg-exploiters.com.
