I wonder if there is a way of disable user-registrations completely? I have a client that is really in no need of adding users. For me that would be an extreme measure of security. Of course I must be able to add users through code or similar.
Is there a way of achieving this?
You can disable your user-registration by routing to Settings > General and then do the following:
Search a checkbox that says “Anyone can register” Uncheck this, so nobody can register on your blog. Now when someone accesses the login page, there will no longer be a “Register” link they can use.
http://www.netwebbing.com/wordpress-user-registration-disable/
Also if you still want a registration page, that's kind of secure. Look at the following: