what is Fast User Switching (FUS)?
This is a technology introduced to Mac users in OS X 10.3 “Panther”. In a nutshell, it allows multiple people to be logged into OS X at the same time, with one user viewing their session at a time. Users have the ability to switch back and forth between logged in users via the FUS menu extra (enabled when FUS is turned on), as well as log in to users that are not logged in yet. Users can also bring up the login screen, allowing only someone with login credentials to get to their opened (or unopened) OS X session. How does this relate to making your Mac completely secure? The beautiful part of Fast User Switching (apart from the gorgeous Quartz Extreme-driven transitions) is that you don’t need two users to apply the security tools of the feature! Even if you’re the single user on that Mac, you can still benefit from FUS by turning it on when you step away from the computer. This way, only you can switch back to your account, in a matter of seconds – and your work is just as you left it
