The Man in the Middle (MITM) attack occurs when a third party element is inserted within the communications path to gain access and/or alter the data being transferred.  It is becoming more necessary in embedded system design to authenticate external connections.  The addition of certificates (https) has helped reduce the instances of MITM takeovers by having a 3rd party verify that websites are in fact legitimate.  Likewise, data endpoints should carry some unique signature that sets them apart from others.  Regardless of the physical interface, perhaps your device should require a code before connecting, or perhaps some other authentication can be utilized. Whatever is decided, two things must be accounted for: 1) how can the MITM attack be prevented? and 2) if the attack occurs, is the data stream encrypted?  Asking these questions throughout your project will lead to a more secure and better designed product or system. -NM