UAC is a Windows 7 in-built tool that protects your system. It alerts you when you are executing some task that requires administrator privileges! For example, if you open a word document and a UAC prompt is displayed, then the document may be some sort of malware as it is requesting administrative privileges when in fact it should not!
UAC runs only with user accounts that have administrator privileges while it does not affect normal users. Normal users without admin rights are by default blocked from running elevated tasks. Do not get mislead by this statement, as there are applications that run with elevated permissions even when normal users are logged on. Therefore, UAC is a security-warning tool that makes you aware of the potential risks.
You can access the UAC window by typing UAC in the Search text box of the Start menu and click the Change User Account Control settings link. Settings are done through a slider that ranges from Always Notify to Never Notify.
The available settings are:
Always Notify: Most secure setting, where you are prompted before programs make changes to your computer or windows settings that require administrator privileges. You must respond to the UAC prompt otherwise your desktop is locked for 150 seconds. This state is called Secure Desktop.
Notify me only when programs try to make changes to my computer: You are only prompted before programs make changes to your computer. You must respond to the UAC prompt otherwise your desktop is locked for 150 seconds.
Notify me only when programs try to make changes to my computer (Do not dim my desktop): You are only prompted before programs make changes to your computer. The desktop is not locked.
Never Notify: Least secure setting, where you are never notified before programs make changes to your computer or windows settings that require administrator privileges.
Why do I get the UAC prompt when adjusting the UAC settings? This security measure ensures that any malware that tries to fiddle with the UAC settings is captured and you are alerted. If you see this message and you have not modified UAC yourself, then some program or malware is attempting to compromise your system’s integrity.