Edit configuration file (ex: httpd.conf)

1) For Directory Listing Showing Apache and OS Information
httpd.conf: ServerSignature Off

2) For Returned By HTTP Response Header
httpd.conf: ServerTokens Prod

BEFORE:

$ telnet localhost 80
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
GET / HTTP/1.0

HTTP/1.1 302 Found
Date: Sun, 16 Sep 2007 07:32:00 GMT
Server: Apache/2.0.61 (OperatingSystem)
Content-Length: 0
Connection: close
Content-Type: text/html; charset=ISO-8859-1

AFTER:

$ telnet localhost 80
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
GET / HTTP/1.0

HTTP/1.1 302 Found
Date: Sun, 16 Sep 2007 07:33:00 GMT
Server: Apache
Content-Length: 0
Connection: close
Content-Type: text/html; charset=ISO-8859-1