I use Nortons IS as my primary protection. On recommends I read on this board, I downloaded the free version of Malwarebytes several weeks back. In the last year, Nortons has only twice reported finding anything. But nothing for many months.
To run Malwarebytes I temporarily disable the firewall and antivirus. I also make sure my laptop is offline. I've run Malwarebytes 4 times. So far it hasn't found anything. Makes me feel marginally better about Nortons, I think. But who knows.