The Echo is basically a home-based device connected to one's home wireless network, right? Well, I discovered today when fooling around with the Echo app on my phone while I was at doctor's office, that I could access my Echo from the doc's Wi-Fi. I did not make the Echo do anything, but when I got home I got on a Wi-Fi that is not my system. I got on the free xfinitywifi furnished by Comcast for its customers. It's signal is all over my neighborhood, (and other neighborhoods around the country) and I can use I when not on my own home system. Very handy.
I was able to select a TuneIn station in the phone app and have the Echo play it when on the xfinity network! OK, so how to tell Alexa to stop playing without asking her to and by only using the app? I found that tapping the pause icon of TuneIn stopped it, but that is not the same as telling Alexa to stop.
Now, I realize that my Echo account is tied to my phone and tablets, so I cannot operate someone's Echo this way, nor can anyone operate mine -- unless they have my phone or tablet. Even so, I am not too happy to discover this undocumented feature of the Echo.
I called Amazon's Echo support and spoke with an "Echo Team" member about my concerns. She genuinely thought this could be a security issue that she will bring up to engineering. She also agreed to contact me when she gets some further info on this situation. She just might do it.
Meanwhile, let's continue to enjoy our Echo.