Mac computers no longer exist, they all use the same hardware now.
The operating system is different, there are several versions of mac operating systems, like there are versions of windows, they all have a low market share.
They may or may not be more secure, the main defense is that people just dont write many viruses for them.
No point in not having virus/malware checkers, good free ones are available, processing power is cheap, seems stupid not to have one installed.