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
The wise make mistakes, the fools repeat them
When you have eliminated the impossible, that which remains, however improbable, must be the truth