Built-In User Accounts
Every installation of Windows 2000 or Windows XP has at least two built-in user accounts that are preconfigured with certain privileges and restrictions:

Administrator. This account has full rights over the entire computer. As a permanent member of the Administrators group, this account has unrestricted access to all files and registry keys on the computer. The Administrator account can create other user accounts.
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Bring back the Administrator account

In Windows XP, the Administrator account normally doesn't appear as a logon choice on the Welcome screen. (It appears only if no other user account exists that is a member of the Administrators, Guests, Power Users, or Users groups or when you boot into Safe Mode.) Rest assured: The account exists. If you want to log on using the Administrator account (or any other account that doesn't appear on the Welcome screen), press Ctrl+Alt+Delete two times to display the Log On To Windows dialog box, in which you can enter any user name.

Guest. The Guest account is intended for occasional or one-time users, and its default privileges are quite limited. A user who logs on using this account can run programs and save documents on the local computer only. In Windows XP, the Guest account can also provide access to shared network resources when the Simple File Sharing option is enabled.
Computers running Windows XP have two or more additional built-in accounts. Unlike Administrator and Guest, these built-in accounts can be moved to a different security group or deleted by an administrator. These additional accounts include the following:

HelpAssistant. The HelpAssistant account, which is used for Remote Assistance sessions, is disabled by default (and protected by a strong password). The HelpAssistant account on the computer belonging to the novice is used for logon by the remote expert.
SUPPORT_xxxxxxxx. Windows XP can include one or more accounts designed for use by vendors such as Microsoft and your computer's manufacturer for online support and service. (xxxxxxxx represents a vendor-specific number.)
If you upgrade to Windows XP Home Edition from Windows 98 or Windows Me, the Setup program might also create an account called Owner, which is a member of the Administrators group.

Windows also includes one or more service accounts—special-purpose user accounts that the operating system uses to run services. (Most Windows-based programs run using the security settings of the user who started the application. Services must run in the context of a particular account, too, but because services can run before a user logs on and can continue running after all users have logged off, they need to use service accounts. The use of service accounts provides control—they have limited privileges—and accountability.) In Windows 2000, most services run using Local System privileges; others run as a particular user or have their own special-purpose user account. Windows XP adds two additional service accounts, with varying privileges. Services can run as LocalService only on the local computer or as NetworkService only on the network.

Libellés : Built-In User Accounts