A: User Account Control is a key technology in the later Windows OSs, including Windows 8. It helps limit normal privileges available during a logon session for privileged users, such as an administrator. It was originally introduced in Windows Vista and prompted users frequently when elevation of privileges was required. The number of prompts was reduced in Windows 7 with a more flexible level of control of the level of prompting in the User Accounts control panel applet, via the Change User Account Control settings option, which the following screen shot shows.
When the setting is set to Never notify, UAC is actually disabled. The same setting is available in Windows 8 (although it has different) text.
However, the changes made to the system are very different from those made in Windows 7 (See also, "Windows 7 UAC Vulnerability Checked"). With Windows 8, the Never notify setting does NOT disable UAC but instead removes any prompts to the user, so when an application makes a request for privilege elevation it will just happen automatically.
UAC is a key part of Windows 8 and required for WinRT-based applications (Windows Store/modern apps) to run. The key point here is when an application asks for elevation, it will automatically be approved; the application still has to be UAC aware and request elevation.
If the application just assumes it has administrator privileges and doesn't ask for elevation, it will fail. It is therefore important to ensure processes such as application installs use a true software deployment system that ensures the correct privileges are available for deployment.
To really disable UAC, you would have to modify the EnableLUA value in the registry at HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System to a value of 0 and reboot, but this is not a supported state of the OS and will block the modern applications-- so don't do this.