Solved Windows Defender Issue

I recently reinstalled 8.1x64 fresh and decided to use Windows own firewall and Windows Defender instead of the 3rd party tools I'd used for years. So far it has worked out, much easier to setup & maintain.

All was fine with Windows Defender until recently with regard to updating definitions via WD itself. I have no idea what the issue is but WD simply quit updating... I open WD, click the Update tab, click the Update button to the right -- nothing, it searches and then nothing. No error message. I updated WD every day via the app since April when I reinstalled. I have no idea what's changed. I will admit I no longer use MU/WU, I'm settled on using 8.1 as is until either I switch to 10, Linux, Apple... I guess my system is possibly missing an update WD needs, not sure? Nothing has changed with the running services, I haven't disabled anything.

What has worked is the offline definitions updater - mpam.fe.exe, whatever the name. I've used it once and it updated WD to the stated versions according to the change log.

Interestingly, if I have the correct log file (mpcmdrun.log), ever since this has happened (about 10 days ago), even after 3 or 4 days without an update the log says "no updates needed"...

MpCmdRun: Command Line: "C:\Program Files\Windows Defender\MpCmdRun.exe" SignaturesUpdateService -UnmanagedUpdate
Start Time: ‎Mon ‎Jul ‎15 ‎2019 05:40:47

Start: Signatures Update Service
Update Started
Search Started (MU/WU update) (Path: Microsoft - Official Home Page)...
Search Completed
Update completed succesfully. no updates needed
End: Signatures Update Service
MpCmdRun: End Time: ‎Mon ‎Jul ‎15 ‎2019 05:40:50

Click to expand...

Finally, I also noticed after using the offline definitions update there's a Network Inspection System Engine & Definition listed in the About dialog of WD...

Hmmm.

Any Ideas?

I don't have an answer as to why Windows Defender quit updating inside the application for a short time, except that it did fail for a time. What allowed me to keep WD updated was using the offline definition file and manually update WD. The file can be found here...

-> Latest security intelligence updates for Windows Defender Antivirus and other Microsoft antimalware - Microsoft Security Intelligence

I needed the Windows Defender Antivirus update for Windows 10 & 8.1 64-bit. Make sure you select the correct product and definition version. I downloaded the file (~140MB) to a USB stick, and ran the file as Admin. I never got a popup, it runs quietly in the background as it's updating WD. I gave it a minute or so to finish updating before ejecting the USB stick.

Here's the definitions change log -> https://www.microsoft.com/en-us/wdsi/definitions/antimalware-definition-release-notes

Like I mentioned I had to manually update but a few times, maybe 3 or 4. I clicked update inside the app just for kicks and WD searched... and found the latest update and updated as expected and is working fine to this day. I will say that MS's servers do have issues periodically, the search fails with a Network Error, trying again in 10 minutes or so works, WD searches, finds, and installs the latest updates!

So far so good.