I was under the impression that the electrics in my totally normal semi-detached house were sufficiently isolated from my neighbours' that it was impossible for my powerline networking adapters to interfere with his. So I was very surprised to find my desktop PC using my neighbour's broadband connection, via my TP-Link AV500. Clearly there is not as much isolation as I had hoped.
The devices have a pair button on them, so I'm willing to believe that there is some security between them. But I'm now concerned that if my electrical circuits are not isolated enough to block the homeplug signal, then is it possible that they are also not isolated enough to prevent power theft?