Information
The <credentials> element of the <authentication> element allows optional definitions of name and password for IIS Manager User accounts within the configuration file. Forms based authentication also uses these elements to define the users. IIS Manager Users can use the administration interface to connect to sites and applications in which they've been granted authorization. Note that the <credentials> element only applies when the default provider, ConfigurationAuthenticationProvider, is configured as the authentication provider. It is recommended to avoid storing passwords in the configuration file even in form of hash.
Rationale:
Authentication credentials should always be protected to reduce the risk of stolen authentication credentials. For security reasons, it is recommended that user credentials not be stored an any IIS configuration files.
Solution
Authentication mode is configurable at the machine.config, root-level web.config, or application-level web.config:
Locate and open the configuration file where the credentials are stored
Find the <credentials> element
If present, remove the section
This will remove all references to stored users in the configuration files.