This is a surprisingly in-depth article over at MalwareBytes regarding just what it is that makes software fall into the category of malware. Finding information or a short definition of malware is easy. Finding this much detail on what is malware, how can you tell when you have malware, how you get it, and more.
Other kinds of malware are a different story. Mac systems are subject to the same vulnerabilities (and subsequent symptoms of infection) as Windows machines and cannot be considered bulletproof. For instance, the Mac’s built-in protection against malware doesn’t block all the adware and spyware bundled with fraudulent application downloads. Trojans and keyloggers are also threats. The first detection of ransomware written specifically for the Mac occurred in March 2016, when a Trojan-delivered attack affected more than 7,000 Mac users.
This is well worth the few minutes it will take to read.