## User Account Control (UAC)

Introduced in Vista, UAC is the "Dimmed Screen" popup asking "Do you want to allow this app to make changes?".

### The Concept
Even if you are an Administrator, you run with "Standard" tokens most of the time. When you need to do a privileged action (like installing software), UAC pauses and asks for the "Administrator" token.
*   **Integrity Levels**:
    *   **System**: Kernel level. Highest.
    *   **High**: Administrators (Elevated).
    *   **Medium**: Standard Users (and Admin non-elevated).
    *   **Low**: Sandboxed apps (Browser tabs).

### UAC Bypass
A common hacking technique. Malware tries to assume the High Integrity token without triggering the popup.
*   **Fodhelper Exploit**: A built-in Windows binary that auto-elevates. Malware hijacks its registry keys to execute code as Admin silently.

### Security Boundaries
Microsoft says UAC is **not** a security boundary. It is a convenience feature. If you are already Admin, UAC won't stop a sophisticated script.