Rootkit/Keylogger Combo

My dad asked me write a keylogger that hides itself with a rootkit.

Give me some suggestions for "undocumented" features.

>>1
Do you have a PS/2 keyboard? If so don't bother writing one, just get a physical keylogger that plugs into the keyboard. Works like a charm.

It's sort of hard to give you ``undocumented features'' when you don't specify what the target OS is. If for windows, you can probably make a really rudimentary keyhook using the SetWindowsHookEx api, with a Dll which injects itself to all running processes, also using the same api.