Win 10 version 1809 has bedded down without problems for over 2 weeks (Build 17763.253), then came the Wednesday automatic updates so system is now on 1809 Build 17763.253. I checked the system cleaner to get rid of the previous version that I may have slightly corrupted, and noticed that the automatic system updates are more comprehensive, including for the first time (I think) the Windows spyware removal tool. The system files cleaner did not list that 20 GB of the old version that I wanted to remove, but did remove the fewer GBs related to update files.
More general question :
I like Windows Defender which plays well with my Avast. I noticed ion my weekly manual check for update, that the last one for Defender was 09.01. It updated once daily normally.
So I wondered why it had stopped. Could it be my over-zealous habit of using the system cleaner, in which I tick all items over 10 MB? Maybe I cleaned out a function that is vital for keeping WD up to date.
I am also thinking of downloading the Windows spyware removal tool as a precaution
https://www.microsoft.com/en-us/download/malicious-software-removal-tool-details.aspx . It is probably also possible to download WD independently, which would possibly kick-start the WD on my system that has stopped.