To disable the “Guest” to appear on the login screen OS X 10.7.2
Open System Preferences
Click on “Security and privacy”
Click the padlock at the bottom and enter the administrator password to open the control panel
Check the box next to “Disable Safari reset when the screen is locked”
This will prevent the Guest user account is displayed in the login screen and the startup and login. Again, it is recommended to maintain this site for security reasons, but if your Mac has locked the safety wire, or if you have no use for Find My Mac, you can delete this and not too guilty.
Disable the user account called Safari on Mac OS X Lion
If you have not tried it yet, click the guest account that gives this message:
This computer will restart in a safe, Safari-only system for the guest user.
The restart process is quick and opens directly into Safari, there is no access to anything else. No Finder, no preferences, no nothing.