Does my mac come with antivirus software

Yes, there is anti-malware software hidden deep in the system. It's part of OS X security. It is updated regularly over the Internet connection or when the OS is updated. It precludes the need to install third-party software for the same purpose. To be sure yours is brought up to date regularly you should set the App Store preferences minimally as:

No, there isn't really a need for it. There are many other security features. The only reason to install anti-virus on a Mac is if you are trying to be nice to your friends running Windows and you do not want to pass something along, something that won't affect you. The downside is most anti-virus packages will slow down your computer. I haven't had an anti-virus application on my computer since 1995.

No

Not outside of the defenses built into the OS; unless you're concerned about Windows malware, you don't need anything else.

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