Everyone wants to run a hugely successful social network but even from day 1, when the site is still being built site owners will find spam bots registering which can be rather annoying.
Some web-masters will turn their site into Maintenance Mode meaning they just see a screen like this:
With this method, everyone is blocked from accessing your website unless they have a valid access code and is very effective in blocking out unwanted users.
Other users wish to have their sites live while only allowing selected users to gain access to the site while avoiding spam signups.
This method is simple to do and can be done via entering your AP > Settings > Signup Process
Select Create Account
Scroll down to the bottom of the page you will see Invite Only
Select this option and click Save.
New Members will only be able to sign up now if you have sent them a Invite E-mail which will contain the Code they would need to join the site.