In 1971 a program crossed the ARPANET and printed that sentence on a teletype. It is generally accepted as the first computer worm, and it was not malicious: it altered no data, and the only effect was the message. The report below tells the story, and the report is the machine the worm runs on. Every pass, Creeper takes the text character by character; Reaper, the first antivirus, restores it. The originals are gone, and Creeper's source code was never recovered. What runs here is a drawing of them.
One full cycle takes about a minute. The text returns exactly as it was; nothing is lost but time. If you would rather read the report without the programs, a plain copy is at ?full=1.
Sources: Wikipedia, “Creeper and Reaper” (checked 4 August 2026); J. Metcalf, “Core War: Creeper & Reaper”, corewar.co.uk. The message follows Wikipedia’s rendering, with a colon; Metcalf prints the same words. Creeper’s source code is lost, so some details rest on two accounts. The page itself is a simulation, not the program; the report above is the part of the page the simulation alters, and it is restored.