User Account Control: Before Vista, Windows automatically gave users too much power over their systems. With User Account Control (UAC), Windows will require a few extra steps before the user can do things such as install new programs. This will make it much easier for administrators to lock down desktops and prevent users, or malicious programs, from messing around with the system.
Windows Defender:Microsoft has built a defence against pop-up ads and unwanted spyware right into the operating system. Although Defender has been criticised for not being as effective as commercial products, the fact that it will be so widely deployed is bound to improve things.
BitLocker: Gives corporate users a way to encrypt and password-protect their data. It can also ensure the OS hasn't been tampered with at boot-up time, but customers seem to particularly appreciate that it will help keep them safe every time a laptop is lost.