This variable contains the comma-separated list of file extensions that will be hidden, i.e. if you configure server to handle files with those extensions by WBSP, WBSP will return HTTP error 404 (file not found). Default value is sr,aut,ic,inc, what means that include files (both inc and ic), subreports and authorization files will be hidden, as long as your server is configured to handle them with WBSP.exe same as files with wbsp extension.