Although shortcuts, when created, point to specific files or folders, they may break if the target is moved to another location. When a shortcut file that points to a nonexistent target is opened, Explorer will attempt to repair the shortcut. Windows 9x-based versions of Windows use a simple search algorithm to fix broken shortcuts. On Windows NT-based operating systems and the NTFS file system, the target object's unique identifier is stored in the shortcut file and Windows can use the "Distributed Link Tracking" service for tracking the targets of shortcuts, so that the shortcut may be silently updated if the target moves to another hard drive. Windows Installer, introduced in Windows 2000, added another special type of shortcuts called "Advertised Shortcuts."