The first message on the ARPANET (the predecessor of the modern Internet) crashed the system.
Sent at 10:30 pm local time on October 29, 1969 by UCLA student programmer Charley Kline, the message text was the word "login." After transmitting the letters "l" and "o," the system then failed. So, the first message over the ARPANET was "lo," and the result was a failed remote login. (Sort of like if Samuel Morse's first telegraph message, "What hath God wrought" had come across as "Wha".)
About an hour later, the computer at UCLA successfully connected and logged in to a computer at Stanford Research Institute. A permanent link between the systems was achieved about a month later.