I'm not picking on Amazon here; it is just that I happen to own a Kindle and shop at Amazon. I do have a Kobo account, Stanza on my iPhone and I've even run into Smashwords and Audible. They all have fallen prey to the same problem. Plagiarism.
Amazon and Kindle positively promote self-publishing. There are over 30 books you can download to get you started, including Amazon's own offering, for free.
Copyright, for the printed word, isn't complex. In most countries the counting begins from the publishing of the work and last for the author's lifetime plus 50 or 70 years - at this point the work becomes freely distributable and can be used (and exploited) by anyone.
The problem arises when it is assumed that just because the author is dead or the book was published 60 years ago it must be a free-for-all.
Take my experience this weekend (and see the links at the end of the article to prove it is far from unique). I had been reading a book called "The End of Childhood" by an author publishing under the name Ibnul Jaif Farabi. I enjoyed the book, a great deal; and did what I always do after finishing a book - went off to recommend it to my friends on Goodreads. Funny thing though, no sign of the book. Time to add it to the database, as has happened before with some Kindle books. Back to Amazon for the book details; no sign of the book. A brief internet search revealed that all was not as it seems. This was not an original work of fiction; it was in fact a copy of "Childhood's End" by Arthur C. Clarke. 'Look Inside' on Amazon confirmed this as even the names hadn't been changed! OK, at least I didn't pay for it, I got it on a free download day, but this isn't the only example - not by a long way.
Project Guttenburg opened up long lost books for a whole new audience; but it has also helped book-thieves profit from the hard work of others. Although these plagarised copies seem to get pulled pretty fast, I'm sure a few quick bucks have already been made at the expense and toil of others. More oversight and checks-and-balances are clearly needed in this emerging market.
You can read more about this issue at these links: