I was extremely pleased to recently learn that the ebook of "Seven Deadliest Unified Communications Attacks" is now available DRM-free through a deal between Syngress/Elsvier and O'Reilly. As I noted in a recent podcast about DRM-free books, this allows you as the reader much more flexibility and freedom in being able to read the ebook on the platform and device of your choosing.
The great part about ordering DRM-free ebooks from O'Reilly is that you can easily get back to your ebooks and download them in multiple formats. They also alert you to updates if there are any.
Kudos to the folks at Elsevier and Syngress for making all of these ebooks available DRM-free!