Hiding an admin user is a fairly straight forward task in Mac OS X. To do so, open Terminal and run the following command:
defaults write /Library/Preferences/com.apple.loginwindow Hide500Users -bool YES
Now, what if you sit down at a machine and you don’t see an expected admin user? Well, use that same command with a NO at the end to (hopefully) bring it back:
defaults write /Library/Preferences/com.apple.loginwindow Hide500Users -bool NO
