As to the identification of hackers, I am not in any way conversant with real computer languages, except they seem to be in some away, **languages.** In addition to being a thriller writer, I am a longtime thriller reader and enthusiast. There has been a trend lately in mid-list (accomplished) authors taking over the books of deceased best-sellers, like the Robert Parker "Spenser" series. These writers are very good, but I can tell within a page that Parker didn't write whatever post-mortem book we're talking about. I can't even explain it, but I know. Recently, the author Lee Child, who writes the "Reacher" novels, turned the series over to his brother, with whom he is apparently quite close. His brother is a talented writer himself, and the first Reacher book by Lee's brother was pretty good, but I could tell it wasn't written by Lee, and I could tell within the first few paragraphs. I know many people, thriller enthusiasts, who can do the same thing, or who will tell me at bookstore appearances that something in such and such a book of mine didn't seem quite like me. And when I look, they're inevitably right. It was me, but not in good form.
I suspect the same is true of code writers. They have a style, a feel, a way of doing things that other experts, who are familiar with them and have studied them, can tell that (say) the Russians are doing it, simply because of style. And style and feel are extremely hard to duplicate, or mimic. In thriller novels, it even comes down to the *spacing* you use between sections. Or the fact that somebody like James Patterson writes short snappy chapters, and somebody like John Connelly doesn't. So, I think it's quite possible that cyber experts could pick out Russians purely on feel.