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Trojan horseIt’s easy to think about viruses as a product of the PC era. But, one of the first viruses ever created affected UNIVAC computers. Although ANIMAL was ultimately a benign creation—a game spread by a separate program called PERVADE—its creator says it was at least partially created to warn others of the potential of a Trojan horse-style attack.

In April 1975, John Walker released PERVADE, which he had designed to spread the game ANIMAL throughout the UNIVAC 1108 system. ANIMAL was like the game 20 Questions. A computer user was asked to think of an animal and then answer a series of questions so the computer could guess which animal.

It was a fun little game, and people began asking Walker for copies. To avoid mailing the game out, he created the PERVADE program to spread the game to every system directory. PERVADE and ANIMAL didn’t cause any harm to the machine. Walker explains on his website: “It spread into successively more protected directories in what today is called a ‘classic Trojan Horse attack.’ In 1975, when I thought of it, I just called it ‘a neat idea.’”

A virus that plays nice

ANIMAL was a small file, and as it updated itself, old copies were overwritten, so the UNIVAC system was not bogged down. “Throughout the entire episode, the ANIMAL phenomenon was viewed with benign amusement by the managers of the systems on which it established itself,” Walker writes. “Lost on almost all of these people was one of my major points, to make them think of what could have happened if I were not a nice guy and ANIMAL an innocuous program.”

A new UNIVAC operating system released in 1976 ended the fun.

Photo: wk1003mike/

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Kate Johanns

Posted by Kate Johanns

Kate Johanns is a communications professional and freelance writer with more than 13 years of experience in publishing and marketing.

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