The number of Mac OS X malware samples detected in 2015 was five times greater than in previous five years combined. Macs are now responsible for 7.5 percent of global personal computer sales. Cybercriminals look at the market and see that the vast majority of folks are on PCs, so they concentrate their efforts on creating malware that will result in the largest return on investment. Adware and malware is getting through on Macs these days is through codesigned apps, using a certificate obtained from Apple.”]
Source: https://blog.malwarebytes.com/101/2016/05/do-i-really-need-anti-malware-for-my-mac/