One Site as a part of Multisite to be hidden (Un-published) from Public?

Lets say i have some sub-domains under one single Multi-site:

• http://ift.tt/1Cln8gx


• http://ift.tt/1BfmWv7 <---- hide from public access (Protected)


• http://ift.tt/1Clna84

How do i HIDE the one site only, from the public access.

(or) Put the site as something like Unpublished (or) dark site?

** HIDE means prevent the "Public" users to see the site. (or) Something like, only the LOGGED IN users via wp-admin (a.k.a) Admins can see the Site and Pages.

Any plugin or approach please?

Thank you so much.