Adding Hidden Categories

Hi,
I’d like to be able to designate a category as Hidden. This would work as Private in that it would never show up in a normal loop, or show up in the archive listing or even be counted…..BUT I want to be able to link to the content in the post elsewhere on the site. Marking it as private won’t work because it still won’t show up unless they are logged in.

I’ve never done any plugin writing and really don’t know where I would start. it seems like a pretty simple thing to do. I know PHP quite well.

Any suggestions ?