There are a number of security and safety features new to Windows Vista, most of which are not available in any prior Microsoft Windows operating system release. There are a number of security and safety features new to Windows Vista, most of which are not available in any prior Microsoft Windows operating system release. Beginning in early 2002 with Microsoft's announcement of its Trustworthy Computing initiative, a great deal of work has gone into making Windows Vista a more secure operating system than its predecessors. Internally, Microsoft adopted a 'Security Development Lifecycle' with the underlying ethos of 'Secure by design, secure by default, secure in deployment'. New code for Windows Vista was developed with the SDL methodology, and all existing code was reviewed and refactored to improve security. Some specific areas where Windows Vista introduces new security and safety mechanisms include User Account Control, parental controls, Network Access Protection, a built-in anti-malware tool, and new digital content protection mechanisms. User Account Control is a new infrastructure that requires user consent before allowing any action that requires administrative privileges. With this feature, all users, including users with administrative privileges, run in a standard user mode by default, since most applications do not require higher privileges. When some action is attempted that needs administrative privileges, such as installing new software or changing system settings, Windows will prompt the user whether to allow the action or not. If the user chooses to allow, the process initiating the action is elevated to a higher privilege context to continue. While standard users need to enter a username and password of an administrative account to get a process elevated (Over-the-shoulder Credentials), an administrator can choose to be prompted just for consent or ask for credentials. UAC asks for credentials in a Secure Desktop mode, where the entire screen is faded out and temporarily disabled, to present only the elevation UI. This is to prevent spoofing of the UI or the mouse by the application requesting elevation. If the application requesting elevation does not have focus before the switch to Secure Desktop occurs, then its taskbar icon blinks, and when focussed, the elevation UI is presented (however, it is not possible to prevent a malicious application from silently obtaining the focus). Since the Secure Desktop allows only highest privilege System applications to run, no user mode application can present its dialog boxes on that desktop, so any prompt for elevation consent can be safely assumed to be genuine. Additionally, this can also help protect against shatter attacks, which intercept Windows inter-process messages to run malicious code or spoof the user interface, by preventing unauthorized processes from sending messages to high privilege processes. Any process that wants to send a message to a high privilege process must get itself elevated to the higher privilege context, via UAC. Applications written with the assumption that the user will be running with administrator privileges experienced problems in earlier versions of Windows when run from limited user accounts, often because they attempted to write to machine-wide or system directories (such as Program Files) or registry keys (notably HKLM) UAC attempts to alleviate this using File and Registry Virtualization, which redirects writes (and subsequent reads) to a per-user location within the user’s profile. For example, if an application attempts to write to “C:program filesappnamesettings.ini” and the user doesn’t have permissions to write to that directory, the write will get redirected to “C:UsersusernameAppDataLocalVirtualStoreProgram Filesappname.” BitLocker, formerly known as 'Secure Startup', this feature offers full disk encryption for the system volume. Using the command-line utility, it is possible to encrypt additional volumes. Bitlocker utilizes a USB key or Trusted Platform Module (TPM) version 1.2 of the TCG specifications to store its encryption key. It ensures that the computer running Windows Vista starts in a known-good state, and it also protects data from unauthorized access. Data on the volume is encrypted with a Full Volume Encryption Key (FVEK), which is further encrypted with a Volume Master Key (VMK) and stored on the disk itself. Windows Vista is the first Microsoft Windows operating system to offer native support for the TPM 1.2 by providing a set of APIs, commands, classes, and services for the use and management of the TPM. A new system service, referred to as TPM Base Services, enables the access to and sharing of TPM resources for developers who wish to build applications with support for the device.