There are currently three types of registration
1) public registration and download allowed: Registration information is accessible from anywhere on the Internet and Internet users can also download the work
2) public registration (no download allowed): The registration information is public, but the copyrighted work can not be downloaded except by the author when logged in.
3) Private Registration: No registration information is available. Only the account user can view information and download the work. Very useful if you do not want to give clues about what you are working on

The three different registration types are equally valid.

The private registration feature is included in Premium and Professional accounts.

The paid accounts can be hired from "My account" - "Professional Services"