phranque - 8:52 am on Mar 11, 2013 (gmt 0)
'HTTP_HOST' => 'www.example.com',
Notice that HTTP_HOST' => 'www.example.com , it should be my domain ?
are you saying the example.com you are seeing for HTTP_HOST isn't your domain?
in any case, the value of HTTP_HOST is the hostname requested, so the visitor isn't changing anything and their requested hostname will only reach your server if you have configured your server to accept requests for that hostname.
HTTP/1.1: Header Field Definitions: