What's the best anti virus software for mac please?
The Macintosh OS has anti-malware software built-in that works mostly automatically and which is regularly updated automatically. It is reasonably effective:
XProtect/File Quarantine/Gatekeeper
Gatekeeper (macOS) - Wikipedia
Safely open apps on your Mac
Mountain Lion: Hands on with Gatekeeper
http://www.thesafemac.com/mmg-builtin/
Just what do XProtect and MRT protect your Mac from?
LockRattler 4.1 for El Capitan, Sierra, and High Sierra is now finally released
So the overwhelming majority of Mac users do entirely without any third party anti-virus software, and yet, you almost never hear of a Macintosh user legitimately complaining that his/her data was damaged by a virus. This is both because there is very little malware for the Mac (about 60 or 70 examples, most of which the Mac OS is now patched against or which is now extinct in the wild; compare this to well over a MILLION for Windows!) and because the Macintosh mostly protects itself.
However, the Mac's built-in malware software looks for very little adware, which is a recent scourge. Adware isn't malicious, it is just really annoying. (It causes your Mac, or just your browser, to show you ads.) This is why folks tend to recommend MalwareBytes, to get rid of adware.
However, I think that folks are mistaken in their recommendation of MalwareBytes. I'm extremely leary of MalwareBytes since they came out with the nagware/commercial version. Download EasyFind and do a search for "MalwareBytes" on your Mac if you have MalwareBytes installed. You will find as many as 24 files (the number, oddly, varies for each user) for MalwareBytes installed all over your system. What do you think that they are all doing? (Hint, MalwareBytes is making money off of you even if you only have the free version.)
I now recommend this instead of MalwareBytes for dealing with adware:
DetectX (free/$10 requested)
https://sqwarq.com/detectx/
Also, while Malwarebytes is a very effective product for dealing with adware (having subsumed the excellent anti-adware product Adware Medic), contrary to what it says on their Web site, it looks for very little actual malware at all and is inadequate for that task.
Don't believe me? Run MalwareBytes. How long does it take to do a scan? About 10 to 15 seconds? Compare that to any decent (or even most worthless) legitimate anti-virus programs, which can take an hour or even much more to do a scan. Malwarebytes can only be doing the most cursory of scans..and it is. MalwareBytes doesn't look inside any files at all. It can only look for specific file names in specific places on your hard drive. It's very easy for malware to hide from MalwareBytes. (It's the same for DetectX, by the way.)
Folks' recommendation of VirusBarrier is a good one.
VirusBarrier Free Edition (free)
Intego Launches VirusBarrier Scanner — Free Mac Antivirus - The Mac Security Blog
Intego VirusBarrier Scanner
This is a full version of Intego's excellent commercial anti-virus program VirusBarrier [usually $40/year] minus some [but not all] of the automated scanning features in the commercial version. This isn't just a nice free product, in the past VirusBarrier has won all the believable third party anti-virus comparison tests.
What ISN'T a good recommendation is Sophos anti-virus. I hear from one or two users EVERY WEEK whose Macs are running like molasses. It's gotten so that I automatically ask first thing if they have Sophos installed, and they almost always do. Once Sophos is removed, things go right back to normal. I'd assiduously avoid Sophos.
So, DetectX and VirusBarrier Free Edition are worth having, and as a bonus they are both free. You really only need to run them if you think that you might have a problem. And chances are excellent that you will never really have a problem that legitimately involves malware. If, like most Mac users, you do absolutely nothing to ward off malware, you should be perfectly fine. That's one of the big reasons we all use Macs!