For your possible interest, here is a current review of the Avast Antivirus program. Jim Hamm has used the free version of Avast for years on both his PC and Mac. He likes it, but it does occasionally do a popup, asking you something, or possibly to upgrade to the paid version. Often enough to be noticeable, but not aggravating -- at least for him. Whether one needs to run an AV program or not, especially on a Mac, certainly has proponents both ways. For Jim, the possible added protection is desirable. Your mileage may vary.