Actually Windows Defender has changed significantly in the last couple of years, recent builds have not changed a ton, at least on the consumer side. The enterprise side (Advanced Threat Protection) has had some "significant" changes, but nothing that would effect what this thread is about. It is pretty sophisticated and one of the leading AV products on the market now. I talked to quite a few other It professionals at other companies at the big Microsoft conference (Ignite) last summer and they agree that it is made some major strides in how well it works compared to others.

I do agree and highly recommend only running one AV product on a computer. The threat landscape has change a lot in the last decade and the modern techniques are needed to detect and stop the bad actors out there. Whatever AV product you use, make sure the virus definitions are up date (daily or even hourly) if you do a lot of online browsing with the computer.

Pete