Whilst it would seem an important concern, especially for authors, when you consider you cannot even protect your personal privacy if you communicate using electronic devices, I don’t see how you can effectively protect something that is published.
Realistically you cannot copyright a sentence, most normal sentences have been used at one time or another by very many. What you can say is that if you put enough words into a long sequence, such as a chapter of a book, then that sequence is unique, but take any small part of it and it probably isn’t, unless it contains made up words.
The only answer for real protection for things communicating via eletronic devices is encryption. By encryption I mean in a way that cannot be broken in a reasonable time scale, like a couple of years or so. This will also protect against hackers. Its quite easy to achieve. What is difficult is to persuade the majoity to use such a scheme, even if they can tailor it to work just between them and their intended recipients. In this scenario then Ebooks and such can be protected and when you buy it you get a unique key to decrypt it.