Thanks to Steven Knapp for his interesting, clear and concise (yes, very clear and concise) description of the IP protection methods. I could not stop reading it. And I have learnt a lot.
But this information reveals the tricks to the copiers :-)

After reading S.K.'s post I think that the best protection for many applications is the use of an auxiliary non-readable device.

An additional idea: Writting the SW in a high level language makes the dissassembled code a little difficult to understand. Therefore the copier can easily make identical copies but not improvements or further development.

Alfredo del Rio.