Use the following steps to disable users from registering and signing up themselves in Joomla. Almost of hackers might try to register themselves as users on the site and try to hack the site, so in some cases when its not required it is essential to turn this feature off.
- Log into Joomla
- Go to Global Users > User options
- Change allow user options to No
- Send Password to No (If you do not want users to re-set their passwords)