Wherever there are barriers there are going to be people looking for ways to defeat them. The Kindle's Digital Rights Management is an obvious target for hackers.
How you feel about DRM (Digital Rights Management) depends very much on which side of the fence you stand. If you are a producer - a writer or a publisher - then it is all that stands between you and piracy that threatens your business model, if not your very existence. If you are a consumer - a reader - then DRM simply restricts your freedom to lend, make back-up copies and resell your ebook purchases. The reader can only look back fondly at the days when books had the sort of physical DRM that they could live with.
Let's face it - currently an ebook places all sorts of restrictions on its use without rewarding the reader with a significant price reduction.
There are always going to be programmers who want to strike a blow for reader freedom and the latest offering is from "TooSmart Guys" in the form of a simple (overlong perhaps) video that shows how to use existing Python scripts to crack the encryption on Kindle titles.
Basically what you do is download (if you don't have it) Kindle for the PC, download and run two Python scripts that decrypt the title of interest. Once you have the unencrypted file you can down load it to your Kindle and use it anyway you like. Notice that the process only works on books you have already bought and it only works on MOBI format ebooks.
However, as with all software security, it is an arms race. Amazon has an alternative format, Topaz, for its Kindle books that, so far, hasn't been cracked in an easy and convincing way. As you might guess, Amazon is quite keen on the Topaz format and becoming keener all the time. Recently Kindle for PC has been updated and the original script no longer works with Version 4. You can of course always go back to the older version but it is quite difficult to avoid an auto-update. The correct solution is to use a slightly different version of the decoding script which is now listed on the TooSmartGuys website for example.
It is sad that the DRM war has to happen at all but until publishers realise that locking their produced behind imperfect digital security isn't the way to go programmers are going to have fun rising to the challenge.