John Walker
John Walker is a computer programmer who is the co-founder of the computer-aided design software company Autodesk, and a co-author of early versions of AutoCAD. In 1975, he wrote the ANIMAL software which self-replicated on UNIVAC 1100 machines: this is considered to be one of the first computer viruses. ANIMAL asked a number of questions of the user in an attempt to guess the type of animal that the user was thinking of, while the related program PERVADE would create a copy of itself and ANIMAL in every directory to which the current user had access. It spread across the multi-user UNIVACs when users with overlapping permissions discovered the game, and to other computers when tapes were shared. The program was carefully written to avoid damage to existing file or directory structures, and not to copy itself if permissions did not exist or if damage could result. Its spread was therefore halted by an OS upgrade which changed the format of the file status tables that PERVADE used for safe copying. Though non-malicious, "Pervading Animal" represents the first Trojan "in the wild".
