Apple uses various systems to protect applications, music and books from its digital stores, but recently an application has been updated and allows the removal of the DRM system of books from the iBookStore. DRM or digital rights management is the general term for copyright protection systems. Apple uses a system called FairPlay to protect its books, but from now on it is useless because it no longer protects Apple's digital products against users who don't want to buy them.
Apple used FairPlay to limit the possibility of playing books from the iBookStore on other terminals than iDevices, but this is now possible. Apple will probably try to re-implement new security measures to protect its books, but apparently it won't be very successful.