The origin of SPAM
In 1937, the Hormel Foods Corporation created a product that was originally called Hormel Spiced Ham. Desiring a more catchy and marketable name, they held a naming contest. The $100 prize-winning entry combined the first two letters of "Spice" and the last two letters of "Ham" to form the now familiar name, "SPAM". The Hormel Foods Corporation has gone on to sell more than 5 billion cans of SPAM and establish an international SPAM Fan Club since then.
Spam as Computing Slang
Most, including Hormel Foods, believe that it is from the song in British comedy troupe Monty Python's famous spam-loving vikings sketch that goes, roughly, "Spam spam spam spam, spam spam spam spam, spam spam spam spam..." The vikings, who were sitting in a restaurant whose menu only included dishes made with spam, would sing this refrain over and over, rising in volume until it completely drowned out the other characters' conversations. Thus spam is supposed to be analogous to large volumes of unwanted traffic that drown out normal traffic.Hormel Foods likes to stress the differences between their product and computer slang by spelling "SPAM" in all capital letters.