if its going to be a non-ficton book then you will have to know your material.. thats a simple fact as infinite said. But if your writing a fictional fantasy hacking book then you dont really have to know anything just have a basic understanding of what hacking is all about.. and the whole scene or else it will be as you said a bunch of crap (which no one will read) but who knows.. post it on dalnet lots of them will read it
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The wise make mistakes, the fools repeat them
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When you have eliminated the impossible, that which remains, however improbable, must be the truth