Earlier this year, my colleague Paul Thurrott (and Rafael Rivera from Within Windows) ferreted out some details about security improvements to Windows 8, namely the addition of Modern Reader, a potentially more secure alternative to Adobe PDF readers. New security features were also revealed during the Microsoft BUILD conference and via a recent blog post by Jason Garms, Microsoft's group program manager of the reliability and security team for Windows 8. I've updated this original post with this new information.

Picture Password
Microsoft previewed a new touch-based security login at BUILD called picture password. Here's how it works: The user selects a picture, then makes three touch gestures on top of the image. The system remembers that sequence, and then the user repeats that sequence of gestures to login. For example, a user could have a picture of a pet as their startup screen, then use touch to draw a smile and touch both eyes of the dog. The gesture is tied to the image, and increases login security considerably. (Microsoft applied for a patent for the "sketch-based password authentication" technology behind picture password several years ago.)

Update: Windows 8 Security Features