The Windows Installer performs a Per-User Installation or Per-Machine Installation depending on the access privileges of the user, the value of the ALLUSERS property, and the version of the operating system.

Windows Vista:  Windows Installer version 4.0 complies with User Account Control (UAC). If the user has user access privileges, and ALLUSERS=2, the installer performs a per-machine installation only if Admin credentials are provided to the UAC dialog box. If UAC is enabled and the correct Admin credentials are not provided, the installation fails with an error stating that administrator privileges are required. If UAC is disabled by the registry key, group policy, or the control panel, the UAC dialog box is not displayed and the installation fails with an error stating that administrator privileges are required.

Windows XP:  If the user has user access privileges, and ALLUSERS=2, Windows Installer performs a per-user installation and uses the folders in the user's profile.

Windows 2000:  The Windows Installer performs a per-user or per-machine installation depending on the value of the ALLUSERS property. If the ALLUSERS property is not set, the Installer does a per-user installation. If the ALLUSERS property is set to 1, the Installer attempts a per-machine installation. The per-machine installation succeeds only if the user has administrative access privileges on the computer. If the ALLUSERS property is set to 2, the Installer first attempts a per-machine installation. In this case, the per-machine installation succeeds only if the user has administrative access privileges on the computer. Otherwise, the Installer does a per-user installation.

If the ALLUSERS property is set to 2, the Installer always resets the ALLUSERS property to null or 1 based on whether it determines to do a per-user or a per-machine installation.

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Build date: 6/5/2008