I have installed Windows 10 as an upgrade to several computers that were running Windows 7. I am generally happy with Windows 10, performance seems to be at least as good as it was with Windows 7 on the same machines, changes to the User Interface are good for the most parts, and it seems to run all the old programs without issue. The upgrade process itself was mostly painless as all the installed programs were still there and working after the upgrade.

However, there is an issue that is bugging the hell out of me. Windows Defender hogs the CPU at random times. To be honest, it is not completely new as I had issue under Windows 7 as well, but it seems that it is much more of a bother to me under Windows 10. The funny part is that Microsoft claims the purpose of Window Defender is to protect your computer from malware and to allow it to run at full speed. Well, in my 25 or so years of using Windows, the worst kind of CPU hogging software I have had on my computer is Windows Defender. That thing starts running at any time, particularly when you use the computer (instead of, say, at midnight) and when it does, the CPU utilization goes to 100% and stay pegged there for hours.

So I went to Google and found this very informative page: http://www.deskdecode.com/antimalware-service-executable-high-usage-fix/

It shows a number of things that can be done to tame the beast and all are good suggestions.