a character that can cast offensive spells, generally the ones that inflict direct damage
A program that damages registry values of your system, a particular program, crucial executable files of the system or program, to disrupt the program or system. A nuker can crash your computer, or make it restart.
An Elementalist focused on doing direct damage to multiple targets. Usually uses Fire Magic.
A program that disables a machine through damage to the registry, key files, the file system, etc.