It is not possible to hack the World of Warcraft servers due to the security measures installed. If you somehow would be possible, you'd face criminal charges.

Smaller forms of hacking are Bots, Cheat programs that rely on server lag, and similar things. These are often found out and blocked by Blizzard, or caught by the game's internal security, Warden.

Warden is World of Warcraft's security program, responsible for monitoring what you have running when you load up WoW. If it sees you running certain programs that help you bot or cheat, it will refuse your login information until those programs are unloaded.