After installing OS X 10.7.2 and enabled the new iCloud services that Apple unveiled yesterday, a number of users have found that the system is displaying a Guest User account at the log-in window.
Upon clicking this account, the system will show a warning that states the system will restart into a Safari-only mode for the guest user, and if any accounts are currently logged in then they will be forced to log out and may lose unsaved work.
For people seeing this, if they go to the Users & Groups system preferences, the guest account will be enabled in a sharing-only mode, but will not be allowed to log in to the system. Unchecking the options to allow file sharing for guest users will change the account to be disabled, but even after doing this the account will still appear at the log-in window.
The reason the guest user account is showing up on these systems is because people have enabled the new "Find My Mac" service that is part of Apple's iCloud. Find My Mac allows you to remotely track and lock or even wipe your Mac. The reason Apple enables a Safari-only option is to allow the computer to still properly connect to the Internet and be used in a limited manner without compromising your data, essentially from one perspective setting a trap for thieves by coercing them into using Internet and location services that will allow you to pinpoint the system. Without this, iCloud will not be able to locate the Mac, and instead only allow you to remotely wipe or lock the system.
Even though this is not a bug in the system and actually can be a beneficial feature, some people may still wish to remove the guest account from their log-in screens. To do this there are two approaches you can take:
- Require username and password
The guest account will only appear as an option if you have your system show a list of users at the log-in window. If you change this to requiring a typed username and password, then the guest account will not be available even if you purposefully use "guest" as the username. Requiring a typed username and password is also slightly more secure than displaying a list of log-in names, since it prevents the display of any aspect of log-in credentials on the system.
- Turn off restarting to Safari
If you go to the General section of the Security & Privacy system preferences, you can check the option to disable restarting to Safari when the screen is locked. Doing this will prevent the guest account from being displayed at the log-in window, but will also keep Find My Mac enabled.
Besides these two options, the last way to disable the guest account is to turn off Find My Mac in the iCloud system preferences, but keep in mind that doing this will prevent you from locating or remotely wiping your system in the event it is either stolen or otherwise inaccessible.