I got that 2 or 3 days ago, just the once. I reckon it's some inconsequential rubbish in chrome, probably caused by an upgrade.
Of course, I might be wrong.
Pretty sure (from memory) you just go to advanced which is below the message and then proceed to the site in question (unsafe). It is not actually unsafe but more of a security issue. I'd ignore it
Been googling, and it is apparently something to do with whether the URL includes https:// or not. If it does, you don't get the warning, if it doesn't you do, which does seem to hold true with my 2/4 pages. Weirdly though, if I open NSC using IE11, NSC does include http:// and the site does not show as "non-private"