(If you don't know my rant on the subject by heart by now, I'm referring to the correct usage of the term, not the bastardization to mean "computer criminal".)
ESR wrote an entry in his blog about Pratchett's hacking exploits as related at his Guest of Honor speech at Penguicon. (Blogspot's permanent links are broken; it's the entry for 5 May.) The Reader's Digest version: Pratchett did a LOT of hacking, both hardware and software, on his ZX-81. Unfortunately for him (but, probably, fortunately for us all), he didn't think that meant he had what it took to do science or computing for a living, so he wrote press releases for a living until his writing took off.