A new feature to Windows Vista is Protected Mode for Internet Explorer 7. This functionality leverages the security model introduced with Vista’s UAC to add a layer of protection to Internet Explorer.

This quote from Microsoft’s website gives a very good overview:

In Protected Mode, Internet Explorer 7 in Windows Vista cannot modify user or system files and settings without user consent. Protected Mode requires the user to confirm any activity that tries to put something on your machine or start another program. By ensuring the user consents to these kinds of actions, the likelihood of automated and/or unwanted software installation is reduced. This feature also makes you aware of what a website is trying to do, giving you a chance to stop it and take time to double check the trustworthiness of the website.

Having used Vista and IE7 for the past several months, this basically means you will get a prompt whenever (among others):

• An ActiveX control tries to either save a file or modify a system setting.
• An external program tries to access Internet Explorer content. I get this when I view the source of a web page using Notepad++.

If you are looking for more technical information about IE7’s Protected Mode, Microsoft has a very informative blog post on their site which gives more details.

While I wouldn’t recommend it, you can disable (and re-enable) this setting by double clicking on the Protected Mode status bar in the bottom of IE7 and selecting the option to Enable Protected Mode as needed.