Here's the grossly oversimplified version:
1) Dmitry Sklyarov, a Russian programmer working for
Elcomsoft, writes a program that decrypts Adobe eBooks into unencrypted PDF format. This is completely legal in Russia, where Dmitry lives and works.
2) Elcomsoft distributes the software to US customers through a US-based partner.
3) Sklyarov attends
Def Con, a computer security / cracking convention, as a speaker. He gives a presentation on the fundamental flaws in the eBook scheme, as well as pointing out that several quite expensive eBook encryption methods sold by third parties are actually trivial algorithms like ROT13. For those unfamiliar with cryptography, this is merely a cipher that rotates the alphabet by 13 letters, and is typically only used as a formality when posting potentially offensive material, or as a toy or joke. A decryption table for it can be made by writing the alphabet in two monospaced lines, and some people can decrypt it in their heads.
4) Adobe complains to the FBI.
5) The FBI arrests Sklyarov on the basis that he has distributed a circumvention device (the eBook decrypting software) prohibited by
Title 17, Chapter 12 (part of the much-maligned Digital Millennium Copyright Act). IIRC, the affidavit for his arrest only indicated that he was the copyright holder of the software, not that he actually engaged in distribution.
6) After various legal BS, Sklyarov was allowed to return home to Russia. However, charges against him have not been dropped, so he is subject to prosecution if he ever visits the US again.