The first ARPANET transmission in 1969 was the two-letter message “LO.” UCLA student programmer Charley Kline attempted to send the word “LOGIN” to the Stanford Research Institute, but the receiving system crashed after the first two letters.
The transmission took place on 29 October 1969 over a leased telephone line connecting UCLA’s SDS Sigma 7 computer with an SDS 940 computer at SRI. Leonard Kleinrock’s UCLA laboratory supervised the experiment, which demonstrated packet-switched communication between separate computers.
Although “LO” was an incomplete command rather than a planned greeting, it became one of the Internet’s most famous beginnings. The full word “LOGIN” was transmitted successfully later that night after the system problem was fixed. ARPANET expanded during the 1970s and became an important predecessor of today’s Internet.