In late 2010, I wrote a short history of Apple Mac malware. Since then there have been some significant developments, so heres a revised and updated version. The first virus to affect Apple computers wasnt written for the Macintosh, but is of historic interest none the less. In 1982, 15-year-old student Rich Skrenta wrote the Elk Cloner virus, capable of infecting the boot sector of Apple II computers. In 1990 the MDEF virus (aka Garfield) emerged, infecting application and system files.”]
Source: https://nakedsecurity.sophos.com/2011/10/03/mac-malware-history/