Explanation/Reference:
Explanation:
Logon HTTP authentication honors the zone security policy for Logon credentials, which may have one of four values:
Automatic logon only in intranet zone. Prompts for user ID and password in other zones. After the user is prompted, this value can be used silently for the remainder of the session.
Anonymous Logon. Disables HTTP authentication; uses guest account only for Common Internet File System (CIFS).
Prompt for username and password. Prompts for user ID and password. After the user is prompted, this value may be used silently for the remainder of the session.
Automatic logon with current username and password. The logon credential may be tried silently by WindowsNT Challenge response (NTLM), an authentication protocol between an end-user client and application server, before prompting.
http://technet.microsoft.com/en-us/library/dd346862.aspx