Elk Cloner was the first virus written specifically for a Mac OSx. It was particularly designed for Apple DOS 3.3. Ever since, every infected Mac OSx has had some form of this virus. The first OSx specific worm was discovered in 2006. There have also been macro viruses spreading on Macs since Microsoft Office for Macs was developed and installed.
In recent news, there are several attacks to Mac OSx systems that have been devastating. OSX/Flashback hit over 600,000 Mac users before it was incorporated into XProtect. By the time Apple’s developers found a fix, they (the developers themselves) were hit with OSX/Pintsized. None of the OSx built-in security feature protections helped ward against the attack. The only way to resolve the malware was to use time machine to restore to a previous point. If time machine was not initiated or updated to include the malware, a new install was mandated. A new strain of malware, identified by VirusBarrier as OSX/Lazarus is an advanced persistent threat (APT). The Lazarus group has ties with North Korea and this APT is designed to leverage zero-day vulnerabilities. The Proton malware masked itself as Symantec software. A variant was discovered, named Calisto, which now masquerades itself as an Intego software installer. Cryptomining is another piece of malware targeted for Mac OSx. Mshelper causes a high CPU because the system resources are being used to mine digital currencies.
Both Apple developers and Microsoft developers have taken measures to harden their operating systems to defend against attacks and reduce the risks of users becoming infected. Both companies encourage users to practice industry standards of applying security updates, hotfixes, and following EOL cycles.