ASP.NET maps the file name extension VSDISCO to an HTTP 
handler that scans the host  directory and subdirectories 
for ASMX and DISCO files and returns a dynamically 
generated DISCO document. 

A client who requests a VSDISCO file gets back what appears 
to be a static DISCO document.

Note that VSDISCO files are disabled in the release version 
of ASP.NET. You can reenable them by uncommenting the 
line   in the <HTTPHANDLERS>section of Machine.config that 
maps *.vsdisco to 
System.Web.Services.Discovery.DiscoveryRequestHandler and 
granting the ASPNET  user account permission to read the 
IIS metabase. However, Microsoft is actively discouraging 
the use of VSDISCO files because they could represent a 
threat to Web server security.