Hey Alan,
So Windows and anti-virus programs go back to the start of viruses. Literally can't separate the two of them, always been an issue, thus why folks have always purchased products like Norton Anti-Virus, McAfee Anti-virus, etc. Mac's had a number of issues back in the System9 days (way back in the 90's, before OS X) but since the move to the OS X operating system has been relatively safe. Part of that is a numbers game, there are just a lot more PC's out there to infect. The other part is that Mac's don't run PC software, so it's requires different .
The current situation with security products is that they're more focused on malware, ransomware and other types of hijacks that either hold your computer for ransom, have you call 'Microsoft' to get them to fix it for a fee, or to be a 'bot' as part of a larger network of infected computers that can be controlled. Mac's have a few security threats, but as a whole Apple does a good job keeping the system pretty clean. This is why you can lock down your Mac to only install software from the App Store, much like on an iPhone. There are some bad software packages out there, but you have to actively install them to become infected. So downloading random software off the internet that claims to be a crack for Adobe Photoshop, or a 'Flash Player update' that pops up on a website is the most common source of infections.
MalwareBytes is a software company that produces a great scanning tool for malware for both PC's & Mac's. The report is a great summary of the types of infections out there, and it shows the types of infections people get.