I am a security professional and have thorough knowledge of macOS internals and the built-in security protections.
Almost all antivirus or security products on the Mac App Store should be treated with extreme skepticism. I recently saw that one of the top grossing apps was an antivirus product called Thor Antivirus. Looking under the hood, it was just ClamAV, and their claims about its protections were unsubstantiated. They probably made tens of thousands of dollars before Apple took them down in response to my report.
Several years before that, I audited SecureMac's MacScan[0], a once-popular antivirus app that had received accolades from MacWorld for years. It turns out it just checked file metadata such as modification times, and didn't even look inside.
Apple's app reviewers are not able identify bogus security products, and the result is that you might damage your system by allowing some half-baked program to run amok.
I don't run any third-party antivirus myself, but when I was investigating a piece of Mac malware, I discovered that Malwarebytes had beat me to the punch and published a great blog post on their investigation. I vaguely recall using their software to clean up a relative's Mac successfully.
By the way, at the time of writing, a program called Antivirus Zap - Virus & Aware is #6 on the Top Paid list of the Mac App Store. Antivirus VirusKiller is #41. I guarantee you they're both shit. (Antivirus Zap also uses ClamAV.)
0: https://web.archive.org/web/20110719013009/http://rgov.org/2...