UAC

(User Account Control) The management of user accounts in Windows Vista. Because malware has greater control of the computer when it is running in administrator mode, UAC was designed to enable more users to run their computers as a standard user rather than as administrator. A computer is more secure against attack if it is running with fewer privileges.

Admin Approval Mode
The default mode in UAC is the Admin Approval Mode, which requires administrators to approve functions that were allowed in Windows XP without a prompt. For example, although standard users are unable to add programs, a user running as administrator does have the right to install new applications. However, in order to prevent unwanted programs from being slipped in "under the covers," the administrator must approve any installation first. See user account, account control and Windows Vista.