Travel back to the 1940s and 50s. Computers are still not widespread, although cybernetics is developing very fast and John fon Neuman has a theory of self-replicating mathematical mechanisms. F.G. Stahl implements the model described in Penrose's article using the machine code on an IBM 650. From the very start, these studies were aimed not at discovering the virus phenomena, but primarily at researching future artificial intelligence. The 1960s and 70s.
Mainframes are now an essential part of every large research institute and military organization.
Programmers experiment with virus-like programs. It's affordable, easy to use, employs powerful development tools and other software. More than 3 million Apple 2 computers are sold. Then the very first anti-virus programs start to be developed. They are very primitive, amateurish, and often freeware.