+ - Shades of Jack Ryan: altering text in eBooks to track pirates->
Seems like I recall reading about this in Tom Clancy's Hunt for Red October when Jack Ryan used this technique to identify someone who was leaking secrets to the Russians. It would be so very difficult for someone to write a little program that, when stripping the DRM, randomized a couple of pieces of punctuation to break the hash that the vendor is storing along with the sales record of the individual book."
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