It is possible to show-hide categories based on your WordPress site user roles. The CaPa Protect is a free WordPress plugin lets allows you to hide or display categories based on user roles types like Editor, Author, Contributor etc. The plugin also provides you the feature of showing a message whenever a someone arrives without permission on a protected blog post of your website. Also you can simply hide everything and your user will not be able to know the existence of hidden post.
Restrict certain posts or pages for logged in users of your WordPress site using a simple admin interface. You can very easily hide few, all or none of your website pages or posts.