User Account Control

User Account Control: "User Account Control
Updated: May 1, 2008
Applies To: Windows Server 2008, Windows Vista
User Account Control (UAC) is a new security component of the Windows Server® 2008 and Windows Vista® operating systems.
What does User Account Control do?
UAC allows an administrator to enter credentials during a non-administrator's user session to perform occasional administrative tasks without having to switch users, log off, or use the Run as command.
UAC also can also require administrators to specifically approve applications that will make 'system-wide' changes before those applications are allowed to run, even in the administrator's user session."