well first of all you made the right thing in stoping the "distribution" of his book.
i've seen threat like that in the moneytec forum too, by the same so called Drforex.
and they stoped the files from being shared.
as for the money he askes i dont know,but i realy dont think you should pay what he asks for.
you should not contact him as he requested firmly with a threatening manner.
i think you should consult with your own lawyer first !!!
dont be intimidated maybe the writer is not him at all and is just a mischievous kid who wants to frighten you.
hell everything can happen in the internet.
you should check out what happend in the moneytec forums with that issue.

here is the link for the disccusion on that matter and how it ended:

the thread called : Have You Also Stolen Bird Watching In Lion Country?

http://www.moneytec.com/forums/showt...hlight=drforex