Just to be clear, this calls the command "rd" (remove directory) with argument /s (recursively remove all subdirectories) and path \ (root of your drive).

Initially it looked to me like a switch called "crd" as argument to the "cmd" command. This would have fooled me into thinking it is harmless. I wouldn't have fallen for "format c:" but I might have fallen for this.

The space between "/c" and "rd" is apparently not necessary. I tested it and it really works.