How To Discover Hidden Commands?

[Nuisance Value]

This is related to my post http://www.hak5.org/forums/index.php?showtopic=17125 but a different approach.

Someone told me there could very well be an undocumented command hidden in WD software to make the disk behave normally. I asked him how to discover such commands but the reply was:

"No way can you discover this command on your own w/o the right hardware & software. I will never discuss details on how to hack such internals. (...). Could I do it myself? Eventually, but it makes no sense to do so, and I doubt that anybody else would even entertain the thought of trying".

So I though I would ask here: how do you discover such hidden commands? Is it some kind of brute force approach, you tell the device 'a', then 'b', then 'c', etc., then 'aa', then 'ab', etc.? Your program listens to the answers and takes note of any unusual answer - anything which is not 'command not found'?

I can code (C/C++ and Perl) but I can't code if I don't know what I'm supposed to tell the computer to do. So any link towards that kind of information would be very welcome.

[moonlit]

One problem with this approach is that you may accidentally run a command which bricks or changes the behaviour of the drive itself. It's also possible that the drive will stop accepting commands under certain circumstances.