In the 1790’s the world’s first national data network was constructed in France and it was a mechanical telegraph system made of a chain towers to communicate with each other.
Two bankers hacked this system and classified the first cyber attack with their acting. It was a clever hack and and showed one things that counts today still:
[…] regardless of the technology, security is like a chain and humans are always the weakest link.
A short read of about 3–4 minutes worth reading.