A potential security threat with all the TCP based network services ts that any one can remotely conduct experiments to know weather a particular service is available. For instance, in an attempt to connect to a certain part on a specific machine (say M), any remote use can check if M is running an SMTP server on part 25. Under this scenario it become easy to find machines that are susceptible to send mail bugs. In order to combat such a potential threat, can u come up with a method thorough wich only authorised users(who passes a certain secret) will bhe able to get response to a TCP SYN packet. Elaborate your method with the help of an example