Clive is conducting a pen-test and has just port scanned a system on the network. He has identified the operating system as Linux and been able to elicit responses from ports 23, 25 and 53. He infers port 23 as running Telnet service, port 25 as running SMTP service and port 53 as running DNS service. The client confirms these findings and attests to the current availability of the services. When he tries to telnet to port 23 or 25, he gets a blank screen in response. On typing other commands, he sees only blank spaces or underscores symbols on the screen. What are you most likely to infer from this?