User Account Control
Most administrators know that users should log on to their computers using accounts that are members of the Users group, but not the Administrators group. By limiting your user account’s privileges, you also limit the privileges of any applications that you start—including software installed without full consent. Therefore, if you can’t add a startup application, neither can a malicious process that you accidentally launch.
With earlier versions of Windows, however, not being a member of the Administrators group could be very difficult, for a few reasons:
Many applications would only run with administrative privileges.
Running applications with elevated privileges required users to either right-click the icon and then click Run ...