I am a long way from an expert, but we haven't had a virus or threat for a very long time. We run Malwarebytes, free, and McAfee. Between the 2, whatever comes on that isn't supposed to, it gets caught.
Dell also suggested we run a cleaner. So, we also run a cleaner--CCleaner, and it is free. It catches registry key repeats, or whatever, and a lot of "junk" that slows down a computer. The CCleaner first analyzes; then you tell it to remove whatever it has found. So, after removal, it always runs faster. To get CCleaner, just go to the browser and type it in, and download. I run it everyday.
Good luck!
Mariah.