History's first public hack: rats, rats, rats
rigb.org
rigb.org
Very few people could even build a receiver, much less tune it.
In a way, that would be like advertising a secure horseback large sign delivery service, where the "security" is that the sender and receiver choose one of a few routes between locations, even though the large sign is easily seen and entirely uncovered, making the courier easily identified and the sign when in transit easily read from a distance. The "hack" for that type of system is ultimately so trivial as to be mostly uninteresting.