Sometime in the early 1970s, the Creeper virus was detected on ARPANET, a US military computer network which was the forerunner of the modern Internet. Written for the then-popular Tenex operating system, this program was able to gain access independently through a modem and copy itself to the remote system. Infected systems displayed the message, ‘I’M THE CREEPER : CATCH ME IF YOU CAN.’

Shortly thereafter, the Reaper program was anonymously created to delete Creeper. Reaper was a virus: it spread to networked machines and if it located a Creeper virus, Reaper would delete it. Even the participants are unable to say whether Reaper was a response to Creeper, or if it was created by the same person or persons who created Creeper in order to correct their mistake.


A virus dubbed Rabbit appeared: it was called Rabbit because it didn’t do anything except multiply and spread to other machines. The name was a comment on the speed with which the program multiplied. It clogged the system with copies of itself, impairing system performance. Once Rabbit multiplied to a certain level on an infected machine, the virus would crash.


Pervading Animal, another game, this time written for a Univac 1108, appeared in 1975. To this day, analysts argue about whether this was another virus or the first Trojan.

The rules of the game were simple: the player would think of an animal and the program asked questions in an attempt to identify it. The game was equipped with a self-correction function; if the program was unable to guess the animal, it would update itself and enter new questions. The new modernized version overwrote the old version but, in addition to this, copied itself to other directories. After some time, as a result, all directories would contain copies of ‘Pervading Animal.’ It is unlikely that engineers appreciated this because the combined volume of the game’s copies occupied a significant amount of disc space.

Was this simply a mistake by the game’s creator or a conscious attempt to clutter up the system? It is difficult to say. The boundary between programs functioning incorrectly and malicious code was unclear in those days.

Univac programmers attempted to use the Creeper-Reaper model to control Pervading Animal: a new version of the game scanned for older versions and destroyed them. However, the issue was resolved fully only when Exec 8, a new version of the operating system, was released. The file system was modified and the game was unable to multiply.