The default is to allow visitors to create an account in Joomla 3.0 and above.
Not all websites need to have registered users, and if your site is like this, then you may want to disable user registration in Joomla 3.0. In this tutorial, we'll walk you through the steps for disabling user registration in Joomla 3.0.
To prevent users from signing up in Joomla 3.0
Log into your Joomla 3.0 admin dashboard.
In the top menu, click Users and then click User Manager.
In the tabs toward the top of the page, click the Options tab
Under the Component tab, find the following setting:
Allow User Registration
If set to Yes, new Users allowed to self-register.
To disable user registration, set Allow User Registration to No, and then click the Save button in the top left of the page.
After disabling the registration option, you will notice that the Create an account link within your Login Form will no longer show, as users can no longer create an account on their own.
Only logins will be allowed for accounts you have manually created in your administration panel.