Hmmm....

How about setting up a "Chip Protecter" linked to a pic pin that is only
used to "Read" the chip. this "Chip Protecter" blows when they try to read
the chip, thus turning off the oscillator, and shutting down the pic.

They can read the chip, but they can't use the same circuit to test it....

(Unless they replace the chip protecter).

another possible approach, is to set up a circuit so that no matter how
the chip is reprogrammed, unless it gets a certain voltage on one of the
pins, it will automagically shut down... can be set up so that it checks
the chip-id to make sure it is on the same chip, or to a timer so that it
will run for about 20 minutes, and then shut down permanently. (blow a
chip protect fuse?)

Of course mis-using this to do planned obsolescence is considered bad
design... isn't it?

                                Grey

GRAEME SMITH                         email: grysmith@freenet.edmonton.ab.ca
YMCA Edmonton

Address has changed with little warning!
(I moved across the hall! :) )

Email will remain constant... at least for now.