UAC(User Accout Control) helps you prevent potentially harmful programs from making changes to your computer.
User Account Control (UAC) notifies you before changes are made to your computer that require administrator-level permission. The default UAC setting notifies you when programs try to make changes to your computer, but you can control how often you are notified by UAC by adjusting the settings.
You can go to Control Panel—User accounts—Change User Account Control settings to open UAC in windows 7.
From the picture we can find there are four type settings for UAC,they are:
Notify me only when programs try to make changes to my computer(The default setting)
Notify me only when programs try to make changes to my computer (do not dim my desktop)