Yes, it does assume trust. I believe that there are third party applications that will improve the security by ensuring that the original session remains locked, and requires a user password to reactivate access.
In response to AObaba's request for a "workaround":
I suspect that the hotkey that will bring up the user switching uses the "Windows Key". You can disable this in the Registry if you want:
http://www.intelliadmin.com/blog/200...s-hotkeys.html
Another approach would be to select your own hotkey sequence rather than the default ;)
I do not accept that this is a "security breach", as it is how fast user switching is supposed to work. I have no use for FUS so I have it turned off.
I can't remember but I think that it is "on" by default? I also seem to recall that the default hotkey might be WinKey + S.
It could be a security issue, however, if your machine is used by other persons whilst unattended. But, I would consider this to be a user created problem, just as if you left your workstation logged on and unattended. The obvious solution is to logout.
I would also point out that fast user switching is supported by Mac OSX and some of the latest Linux distros, but I do not know if they behave the same as Windows.