In 1988, ARPANET saw its first widespread infection by self-replicating code: Morris, a worm that could install multiple copies of itself on the same computer, causing infected systems to grind to a halt. As the Morris worm began to spread in the United States, Spilling's American colleagues called to warn him. Faced with a threat to his nation's entire network of computers, he acted quickly and disconnected Norway from the rest of the Internet, which at the time could be done by unplugging a single cable.[3][4]