Originally Posted by JSWolf
When you purchase a Mobipocket format eBook, the site you purchase it from has to talk to the DRM server in order to insert the PID(s) you've told the site you want to use. So in effect you are sending your purchase info back to Mobipocket.
Ah, I didn't know the encoding was such a secret that it wasn't provided to Mobi stores as an SDK. Well then, that makes sense that they could get the info from the PIDs.