There's no feature of Windows Vista more loathed than the User Account Control (UAC) security feature that pops up every time you try to do anything. Here's how to permanently disable it (and possibly regain your sanity in the process).
If you've ever tried to install software on a Vista machine, you'll have encountered UAC — the pop-up dialog that fades everything else into the background and asks you to confirm if you want to do something. In many cases, you'll get a warning dialog telling you that you're about to see another warning dialog. Any activity that will result in a UAC dialog will typically be marked with the Windows security shield symbol (as pictured in our Outlook example).
There's no doubt that UAC makes it less likely that you'll inadvertently install malware, and can help secure systems for newbie users. However, it's a poorly conceived system because it's way too sensitive — many of the options you might regularly access from Control Panel will result in a UAC prompt, for instance. This is bad both for power users (who get frustrated by being endlessly asked if they want to do the thing they just asked to do) and for regular users (who are likely to end up routinely clicking yes on all UAC prompts without actually thinking about them).
Because Microsoft continues to believe (despite the overwhelming evidence) that UAC is useful, it makes getting rid of it relatively obscure and difficult. But if you're confident that your machine is secure (make sure you've got good malware protection and effective passwords), disabling it can be a useful step
Shut down any open applications (you're going to have to reboot, which is often slower if you start with multiple applications open).
Open the Vista User Accounts control panel (search for User Accounts from the Start menu, or find it via the Control Panel link).
Click on 'Turn User Account Control on or off'. You'll receive a UAC prompt, and if you're not logged in as an administrator, you may be asked for an administrator password. (If you don't have the administrator password for your PC, you won't be able to switch off UAC.)
De-select 'Use User Account Control (UAC) to help protect your computer'.
In typical Microsoft fashion, you'll be told you need to reboot. Click on Restart now to finish the process. You'll also immediately see a security warning pop up on your toolbar telling you UAC was switched off.
More nuanced approaches
While Windows 7 hasn't ditched UAC, it has made one massive improvement to it: you can now specify what kinds of activities result in a prompt. While the Windows 7 default is still nag-you-until-you-scream, you can choose an option that notifies you when programs try to change your system, but not when you make changes yourself.
If you're still on Vista, there are other options if you want a degree of control over UAC but don't want to disable it entirely. Norton offers a free replacement UAC, and freeware program Elevator lets you disable UAC prompts for specific programs.
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