Here's an interesting story of how some traders hacked the telgraph system in France, to get advance knowledge of market movements...

https://www.1843magazine.com/technology/rewind/the-crooked-t...

There is a good book called The Victorian Internet that covers the development of long distance communication up to the electric telegraph. People did all the same stuff with it. Front running trades and horse races, hooking up with other telegraphers. I can't remember all the details but it was fascinating how much of it paralleled the early internet.