BitLocker Drive Encryption is a full disk encryption feature included with the Ultimate and Enterprise editions of Microsoft’s Windows Vista and Windows 7 desktop operating systems, as well as the Windows Server 2008 and Windows Server 2008 R2 server platforms. It is used to protect all files stored on the drive Windows is installed on. It encrypts the entire system drive and helps block hackers from accessing the system files they rely on to discover user passwords. By default it uses the AES encryption algorithm in CBC mode with a 128 bit key, combined with the Elephant diffuser for additional disk encryption specific security not provided by AES. BitLocker also prevents hackers from accessing the hard disk by removing it from a computer and installing it on a different computer.

BitLocker is available only in the Enterprise and Ultimate editions of Windows Vista and Windows 7. Users of other versions of Windows Vista could use a 3rd party encryption program to satisfy the need for full drive encryption.