Just to clarify, as someone seeing "instead of wifi" and "acts as a large antenna" from the parent comments may come to an incorrect assumption.

In PLC (power-line communication), wiring is not meant to act as antenna. All transceivers are wired. It's an undesirable, unintentional side effect of limited (to the extent of complete lack of) cable shielding - because, well, power lines are usually meant for different application than data transfers.

Thanks for replying and pointing that out. I've corrected my comment.

So am I basically broadcasting my data to anyone nearby with a receiver?

They're encrypted (or should be), so no.