Then you can limit hacking to those that can get their hands on a memroy wand.

The problem is, when you have thousands of your product out in the field, that header block in the wrong hands can wipe out your market until you accept returns/repairs as you program a more protected system.

Basically you've got a thousand locks ou in the field with one key. Once the key is copied, you have a potentially big problem.

I would recommend some serious thought to the support of unique keys for each serial number. You can base it upon an algorithm that uses the serial number to generate a key but this is less secure. However this is acceptable if there are fewer units in the field.

A more secure solution is to randomly assign keys to each unit manufactured and keep those records for future updates. Plan on redundancy copies and a data safe. Avoid the mistake commonly added: A Field Service Master Key... that's all the hacker needs and they commonly ARE fired field service personell.

duh