In my computer repair business, I am still getting W10 computers with all kinds of bad viruses when their Owner's completely rely on Windows Defender alone.
If they add a good antispyware program such as Malwarebytes (mentioned twice above), I still get infected computers. Some customers have tried SuperAntiSpyware, another well-rated program; but those programs together don't stop everything.
Of course it's up to you; but the old saw
"you get what you pay for", really applies to AV programs!
I disagree with both of my esteemed colleagues on this issue; I've been seeing this occur for the last 20 years ever since Microsoft decided to include an AV program built-in to Windows. So, regardless of what you read on the Internet or hear from friends, colleagues, family members, or co-workers: don't believe it!
If you talk with any good Computer Tech who owns his own business and has been in business for at least 15 years; they will tell you the same thing.
I'll tell you what I tell my Customers; since viruses and malware really started being a threat to the average home computer user back in 2003 (14 years ago), I since developed my own formula and never ever rely on
WD (Windows Defender) or the older
MSE (Microsoft Security Essentials). Here is what I install on every computer *except a few* I touch, repair, or install:
1.) Avast AV Free or Paid 2016
2.) Malwarebytes Free*
3.) TrendMicro HouseCall online scanner*
4.) TrendMicro RooKitBuster*
5.) TrendMicro RUBotted*
6.) TrendMicro Browser Guard (Avast SafeBrowse can be substituted for this in W10)*
* These are Backstop protection and do not replace or interfere with the Primary AV program, either Avast or Norton. I have several other Computer techs who own their own businesses have variations on this theme; but virtually every one of them no longer relies on Microsoft WD or MSE to protect their Customer's computers or their own for that matter.
Bear in mind, one of my long time hobbies is building computers that attract viruses so I can figure out how to block them and keep them out of my own computers as well as my Customer's computers. In other words, I collect them and then report and send them to the major AV companies. This includes
F-Prot, Symantec-Norton, NAI-McAfee, and Avast primarily. So for me it's vital that I protect my computers and those of my Customer's from the Internet scourge of viruses/malware. I typically have a 98% non-return rate with my AV protection formulation above using the free Avast version (
less than 2% return rate due to infection), and a 99% non-return rate (
less than 1% return rate due to infection) with the same formulation using one of the Avast paid versions (either Internet Security or Premiere) or substituting Norton Security Deluxe (used to be Norton Internet Security).
These numbers are based on my own customer-base of about 250 customers in my location. Each Tech or Repair Shop Owner will have different numbers, so they are only subject to what I'm telling you. You can choose to believe or not.
I can also tell you that I've repaired, upgraded, and installed about 2 dozen W10 computers since they became available to buy in stores back on July 29th 2015, and these same infection-rate numbers apply. Most of these Customers have had earlier versions of Windows going back to W98 or W95 and had relied on using Microsoft's built-in AV protection programs; and in just about every case, they had gotten infected by 1 or more nasty viruses to the point where their computers became unuseable and had to get them professionally repaired. My take on this, is that W10 Defender is not much improved over their earlier versions of AV protection. This is not just 1 or 2 computers that I own that have never gotten a virus using Defender or Defender+Malwarebytes; but many W10 computers; desktops & laptops made by several different makers (Dell, Acer, Gateway, ASUS, Lenovo, Samsung, and Toshiba). I have published an earlier version of this protection formula on this forum and other forums, but this is my latest and best combination. I've delayed publishing it as I wanted to make sure it was performing solidly on W10.
Once again, to be clear, this is only MY opinion and does not represent the official opinion of Windows Forum at all. Whichever protection method you choose, best of luck to you!
Hope this proves insightful for you.
<<<<BIGBEARJEDI>>>> 
It's interesting that on machines that have had Windows reset or completely reinstalled, I don't see the kinds of Blue Screens you often see on the self-built and custom-built machines that OP's often post here.
But, thanks for posting as often end users do not believe me when I tell them WD is just not going to cut it. Especially, if you are a User that frequently visits "questionable" websites!! Thanks for posting regardless.
