Requests for new logins
There is the single command that blocks newcomers from creating user names and lets you generate their usernames along with their email address. You give them an initial password which they can later change. As sysops you can delete or block a user.
# Prevent new user registrations except by sysops $wgGroupPermissions['*']['createaccount'] = false;
Instructions at http://intersci.ss.uci.edu/wiki/index.php/Restrict_account_creation with a link to mediawiki
I have had no problem with this since I found this solution to our hackers.
You simply go to main sidebar menu "Special Pages" then to Log in / create account and as sysops you do the account creation, and email that person their account name and the password you created for them.