[troyhunt]

It's harder to detect the framework when ASP.NET MVC is used. No view state in the source code, no .aspx extensions and the server response headers identifying IIS and ASP.NET can be removed. There's always HTTP server fingerprinting but you're moving on past the low-hanging fruit now.

[pbz]

Well, after removing all the default headers, there's the CSRF token, certain paths that will bypass a regular 404 detection, and so on... There are ways.