I've got some software which I am considering marketing in Cambodia, 
but I need a good way to keep it from being pirated so that I can 
sell more than one copy. Would it be possible to have the program 
generate a number for the user to send me based on both the serial 
number of the program and the serial number of the computer? Is there 
such a mahine serial number? What about the "Customer Care Code" in 
the Apple system profiler?

When a user sends me this number, then I could generate the unlocking 
code from it. If it was derived from the machine serial number, then 
the unlocked copy couldn't be used on any other machine. And, since 
the serial number of the program would also be in the number the user 
sent me, I could tell if that copy was being put on a lot of machines.

Or is this whole machine serial number just a figment of my 
imagination? Would I have to use some other distinguishing feature of 
the machine?

Thanks.
Anders