The number of malware that can infect Mac computers has increased significantly last decade (2010-2019), particularly scams (including tech support scams) and fake anti-malware apps. since when malware for Mac computers did exist?
The first viruses for Mac were targeting Hypercard. The first Hypercard virus appeared in about 1991. Hypercard has a scripting language called HyperTalk, which was powerful enough to perform file-system accesses, thus allowing Hypercard viruses to discover and spread to other stacks (HyperCard "documents").
The very first virus might have been
- nVir of 1987
Although technically not one, nVir worked much like a boot sector virus. Its source code did circulate on BBSes very soon after, leading to short flooding of copies. Still the damage was rather small. Not much later
- HyperAvenger of 1988 (also called Dukakis-Virus)
made its debut. It was based on HyperCard and became much more visible than nVir - after all, HyperCard was kind of a hype at the time.
During the mid 1990s a series of Word- and Excel-Macro virii did plague the Mac community.