A problem of proportions is the one that several users are reporting and that the Windows Latest site picked up, since a system update would have caused a break in the Defender antivirus, making the defenses against malware absolutely unusable.
It turns out that after doing the respective scans of the program, several users are receiving the following message:
"Item skipped in scan, due to exclusion setting or network scan disabled by administrator."
The problem that is specific to Windows 10, occurred in Windows Defender version 4.18.2003 or later, apparently introduced this error when Microsoft was trying to fix other problems.
I get that message with a manual quick scan or a full scan. It happens if I turn off the Cloud Protection delivered or Controlled Folder Access or not. I did not test the other settings. I do not have any excluded folders, a user reported in the usual questions to Microsoft.
Similar were the complaints of another user on Reddit. It seems that something made the notification settings with the last update get strange. I then scanned with malwarebytes and found nothing. I also did an sfc / scannow and found a corrupt file that seems to be related to OneDrive but seems to be unrelated.
As Windows Latest has put it, "Windows Defender Antivirus scans are skipped due to item exclusion or network scan settings."
This is because testing Windows Defender offline can be done correctly, indicating that it is due to a problem in the upgrade.
On the Answers.com forum, a user claimed about the problem that I did a full re-installation of Windows 10 from a USB key. The problem disappeared until I updated Windows with patches B4551762 and KB4537572 (which I think is the NET Framework update). Then the problem appeared again. I think it could be update KB4551762 ?.
It is not the first time that Windows Defender has a problem with updates, since something similar happened in 2019, causing certain problems in the normal virus analysis on the computer.