When you install Windows Server 2008, the operating system installs default users and groups. These accounts are designed to provide the basic setup necessary to grow your network. Three types of default accounts are provided:
Built-in. User and group accounts installed with the operating system, applications, and services
Predefined. User and group accounts installed with the operating system
Implicit. Special groups, also known as special identities, created implicitly when accessing network resources
Although you can modify the default users and groups, you can’t delete default users and groups created by the operating system because you wouldn’t be able to re-create them. The SIDs of the old and new accounts ...