The Services Directory provides a browseable HTML-based representation of all your ArcGIS Server web services and the actions you can perform on them through REST. The Services Directory can be a useful development tool; however, Esri recommends that you disable the Services Directory for production systems when you don't want users browsing your list of services, finding your services in a web search, or making requests to your services through HTML forms.
Use the ArcGIS Server Administrator Directory to disable the Services Directory.
- Open 
the Administrator Directory and log in with an account that has been granted administrative privileges.  The Administrator Directory URL is in the form http://gisserver.domain.com:6080/arcgis/admin. 
- Access the Services Directory settings by clicking system > handlers > rest > servicesdirectory > edit.
- Uncheck Services Directory Enabled and click Save.