The next e-book you buy might not exactly match the printed version. And those changes are there to make sure you’re not a pirate.

German researchers have created a new DRM feature that changes the text and punctuation of an e-book ever so slightly. Called SiDiM, which Google translates to “secure documents by individual marking,” the changes are unique to each e-book sold. These alterations serve as a digital watermark that can be used to track books that have had any other DRM layers stripped out of them before being shared online. The researchers are hoping the new DRM feature will curb digital piracy by simply making consumers paranoid that they’ll be caught if they share an e-book illicitly.

Current e-book DRM restricts the movement of e-books between stores and devices, and ties a book to a single account. A e-book bought in the Kindle bookstore, for example, will only work on a Kindle. The same is true for books bought in the Barnes & Noble and iBooks digital bookstores — they’ll only work on the Nook or Apple devices, respectively. This makes publishers happy because their books are locked to one person. And it makes digital book vendors happy because it keeps readers tied to their proprietary devices and ecosystems.