I remember that from an economics class. That is definitely a way of adapting the model to prevent piracy -- kind of like how desktop software is easy to pirate

I remember that from an economics class. That is definitely a way of adapting the model to prevent piracy -- kind of like how desktop software is easy to pirate, but SaaS isn't. The electronic component needs to be actually useful to be adopted by teachers. I've bought other books with some kind of electronic component (chemistry, physics), but I never scratched off the keycode to maintain the resale value of the book. Economics is the only class I've had where the software component was required to complete the homework. Damn capitalists. The biggest barrier to book piracy being useful is new editions. Often older editions (and older solutions manuals!) are available online, but in engineering, at least, they change the order of the problems to deprecate the old editions.