Anonymous authentication handles client requests that do not contain a user name and password. Each Internet Information Server service maintains a Windows NT Server user name and password for these anonymous requests. You can view and set an anonymous logon user account in the Internet Service Manager Service Properties dialog box.
During setup, Internet Information Server creates the IUSR_computername account for anonymous connections. For example, if the server name is SERVER1, the default anonymous user name is IUSR_SERVER1.
Internet Information Server Setup creates the same anonymous logon user account for all Internet services. But Internet services can use either the same anonymous account or different accounts.
In the Windows NT Server security model, every user account has a unique security ID (SID). Windows NT Server tracks permissions through the SIDs. Permissions are recorded within an Access Control List.
For anonymous requests, NTFS grants permission based on the request's Access Control List. If the ACL does not assign these permissions to the anonymous logon user, then the request fails. If the server file does not grant permissions to an anonymous user account, you can eliminate the chance that an intruder might access a server file by selecting only the Allow Anonymous option in the WWW Service Properties dialog box.
You can set the Internet Information Server WWW service to respond to failed anonymous requests by selecting the Windows NT Server Challenge / Response option in the Service Properties dialog box. In this case, the server asks for a Windows NT Server user name and password. An intruder can take advantage of this to gain access to a server.
Because the Gopher service offers a published menu, it requires only anonymous authentication. You should configure FTP and Gopher users for the network logon mode. However, the FTP and WWW services also provide file and data transfer, which requires a higher level of anonymous security.
Note
Do not use the network logon mode if you are using a remote SQL Server with Integrated Security, or any other second-level server that requires authentication. Although the network logon mode allows a user to access the primary Internet server, the primary Internet server is unable to authenticate the user for a remote or second-level server.