UAC stands for User Access Control. User Account Control (UAC) is a feature in Windows that can help prevent unauthorized changes to your computer. UAC does this by asking you for permission or an administrator password before performing actions that could potentially affect your computer's operation or that change settings that affect other users. When you see a UAC message, read it carefully, and then make sure the name of the action or program that's about to start is one that you intended to start.