Where does powerline networking end?

Powerline adapters are popular as solutions to wifi range issues in homes... but where does the powerline network access end?

For example, when using them in a single family home with its own electrical panel, is the network accessible beyond the panel... e.g. next door.

I know you can encrypt the signals, but still wondering what the exposure is once you start using these devices in a home.

Thanks for any info or direction anyone can provide.

Tomster2