Server should sent 404 http response. How?

Hi,please help.

Web users can send a special tag named “X-moz” in the HTTP header. How can i prevent access for all the users are sending this tag?

Concept:

  1. with GetHTTPHeader() i can read the X-moz tag.

  2. if X-moz tag is set, server should sent a 404 HTTP response

How to implement 2) ?

Has anybody any idea?