But it was not called “hacking” back then: it was called “scientific hooliganism”.
Marconi’s invention posed a threat to the wired-telegraph industry. In response, the Eastern Telegraph Co. hired John Nevil Maskelyne, a British magician and inventor who had experimented with wireless technologies, to monitor Marconi’s work. According to an article in New Scientist, Maskelyne was able to build broadband receivers capable of intercepting Marconi’s so-called secure transmissions without knowing their frequencies.
In June 1903 Marconi held a public demonstration in London to show how his device could receive a message from a station nearly 500 kilometers away. But before he could receive the message, an intruder delivered this to Marconi’s receiver:
Rats rats rats rats.
There was a young fellow of Italy,
who diddled the public quite prettily.
The message went on to further mock and insult Marconi.
Source: A History of Hacking