One who thinks he/she has done something brilliant by hacking another, when really all he/she has done has ruined a perfectly useful space of time annoying another user with his/her pathetic, destructive behavior.

An "Elite Hacker."

It's usually just some retard who thinks he can hack you.

One who uses cheats or hacks in online multiplayer games such as Counter-Strike. The cheater often has an aimbot, can see players through walls, uses neon colored player models, and has decreased recoil to name a few advantages.