A consumer (i.e. workplace for people who don't know better) NAS is usually Linux with a few hard drives attached via a cheerful and brightly coloured web UI - occasionally useful, some way short of secure.

I expect someone sells hardened ultra-secure corporate NAS boxes, but I've never seen any in the wild.

The trouble is, the sort of people who would buy a pre-hardened NAS are also the sort of people who would be suspicious of a pre-built unit. I know for sure I wouldn't trust anything off the shelf, I'd take the base OS and build something around it.

Whoops, my tin-foil hat appears to have slipped.