[dhtns]

I'm not sure which specific Kevin Mitnick book you're actually referring to or looking for but the book "Underground" is actually by Suelette Dreyfus and is about the nascent hacker/cracker subculture of the late '80s and early '90s. It was researched by/with Julian Assange (not written by him as another commenter has stated) who is known in the book as "Mendax". [1]

Interestingly, the book was released for free online in 2001, at the suggestion of Julian Assange, and the author credits this online release for expanding both the quantity and range of different people that would end up reading the book. [2]

The book can be read online (in HTML) at [2] or various ebook formats can be downloaded from Project Gutenberg at [3].

[1] https://en.wikipedia.org/wiki/Underground_(Dreyfus_book)

[2] https://suelette.home.xs4all.nl/underground/justin/preface.h...

[3] https://www.gutenberg.org/ebooks/4686

[KlaymenDK]

Yes, this must be it. Thank you (and other commenters!) for the added references.