(If this is in the wrong section, sorry. It kind of spans hardware and software.)
I'm liking the Arduino so far, and it seems inexpensive enough (especially the Pro variants) that I could see myself using it en masse to produce useful gadgets and doodads.
However, since some of these gadgets and doodads may be more security-sensitive than others, it would be extremely useful if I could restrict reprogramming of the board (so that only authorized firmware upgrades can be applied, for example), or failing that, to disable reprogramming entirely (not as preferred, but better than nothing) while still having the program on the device work as it should, and for the current program to continue working.
Are there any (comparatively) simple modifications to the board that can achieve this? For sake of reference, I'm using a Nano to prototype, and will be using one of the Pro boards if I ever, well, go pro.