Google uses robust security measures to protect books available for preview in Google Books, and we will continue to do so for books available for sale on Google Play. Once a book is purchased on Google Play and is added to a consumer's bookshelf, it can only be accessed when the consumer signs into his or her Google Account
Each consumer's book on Google Play has a unique coding that caches the book when it is accessed through a browser (as opposed to a digital download; see more information on file protection). This means that the book is broken down into fragments and temporarily stored in -- and accessed through -- the browser window. The Google Play web experience for books, therefore, is not that of a file download -- it is an experience that is optimized for reading in the browser. This allows Google to detect and protect against abuse of each book on Google Play.
Buyer authentication and access
All buyers must have Google Accounts in order to purchase books on Google Play. We have well-established security measures in place, used by all Google products, to help keep users' accounts secure.
There is no expiration date for online access to books on Google Play. As long as the buyer does not request a refund for the book (generally an option for seven days after sale), the book will remain accessible.
However, if a user tries to access a book on Google Play on a number of devices at the same time, our system may temporarily block them from opening new reading sessions.