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If you delete an account, the account must be gone. No login possible anymore. Otherwise it's not deletion.

Are there any books of this kind for modern languages?

It turns away more potential customers. The DRM has helped absolutely nothing to protect against copying. The book is already out there on the net as a now "DRM-free" PDF. It's a shame that illegally downloading it is currently the only way to get the format that many customers would be happy to pay for. If I were the author I'd hurry up and quickly put a DRM-free version on a service like Leanpub.

They don't protect anything. Probably 90% of your catalog is out there on the net and findable with a bit of googling. In the end it's just a bad business decision. You scare away potential customers and your stuff gets pirated anyway. You're degrading your own product and artificially creating a situation where the pirated product is actually a better one (one without a watermark) than the one you are legally selling. You've got to realize how insane that is.

The watermarking is the sole reason I don't buy ebooks from PragProg.

A digital watermark is automatically inserted customer information into a purchased product to restrict it's usage only to the buyer of that product. To me that's exactly like Digital Rights (Restrictions) Management. Calling something that contains digital watermarks DRM-free is deceptive to the customer. But long story short, if it contains watermarks I don't buy it.

Watermarking puts the liability (maybe not legally) on the customer to protect the files from any third party access because there's always the risk that someone who gains access to them puts the files on the net with your name/email or user id on it. This is something no customer can realistically ensure and to me this is a huge restriction to the usage of the books. Second it's ugly as hell to have the watermark on every page. Third it sends the message to me as a customer that I'm not trusted. WTF dear publisher. I want to buy your ebook although I could find 90% of all ebooks for free on the net. Why do you think would I do that if I didn't want to support your business? You watermarking publishers need to realize that by watermarking you create a defective product. The people who pirate your books get a better product, one without a disgracing watermark. Whenever something like that happens, where the pirated product is better than the legally purchased one, it is a clear indication that the anti-piracy mechanism should be dropped. Big respect to Tim O'Reilly and Bill Pollock who are two of the few people who have fully understood that.

O'Reilly, NoStarch, Packt and Leanpub books are fine since they're completely clean. But books from Pragmatic Programmers, Manning, Apress, Addison Wesley, Pearson and Sams are watermarked which I consider just as bad as DRM. I never buy digital books from publishers who watermark.

Dammit, the epub format is such a disgrace for books, especially for those containing code snippets. I've yet to encounter a book that doesn't suffer from being published as epub. I prefer a well formatted pdf that just looks like the printed book, any time.