Peter:
The very best way to offer your customers a product that has high security is to present it with the following attributes:

1) Use the standard security bits scheme on the microcontroller to discourage the average casual hacker.

2) Offer impeccible customer service on the product so that your customers will be very loyal and not willing to look for product from a lower priced competetor that may have copied or stolen your product idea.

3) Offer the product with as many options that you and/or your company can affort to support. With options you defeat the hacker and product copy artist becasue you make their work to keep up with you a nightmare. It is even better if you use ISP based FLASH for the embedded firmware and have seperate firmware sets for each option of the product so that it appears to the copy artist that you have "N" sets of hardware/software.

4) Stay aggressive in releasing new versions of code and options that keep the project modern, up to date, and with handy new features. All the better if these updates are software only updates which just need to have the product FLASH re-programmed. (I.E. give your customers a utility for their PC to reprogram new firmware into the product after they have downloaded and paid for the new software release off your company WEB site.

I hope this ideas help.

The basic idea this is to move technology faster than it can be duplicated.

Michael Karas