Secure Boot. Intended to prevent malware from infecting computers during the boot process before Windows and its other built-in safety features kick in, Secure Boot confirms that all components contain appropriate security certificates before allowing them to launch.
Improved BitLocker drive encryption. Microsoft first introduced this feature with Windows Vista. The new version only encrypts the parts of the disk that are actually being used, speeding up the process.
Smartscreen Application Reputation Service. This feature lets users know whether an app they try to download is unsafe by comparing the app to known reputation data.
On the networking front, Windows 8 includes improvements to DirectAccess, a mobile access technology and VPN replacement first introduced in Windows 7. It also features Branch Cache, which aims to save bandwidth by speeding up the access of remote files stored on a corporate network.