Norton may have broken Windows Defender royally

Norton 360 for Windows
1

Note: I know Norton traditionally doesn’t allow windows defender to run while Norton is running. But I know you can access periodic scanning and even do protection updates and quick scans and such.

So, starting last night, I opened Windos Defender and ran protection updates, which updated me to the latest Windows Defender version. Since then, I get several errors with Windows Defender whenever I try to open it during periodic scanning. It stays open for a few seconds, then cuts off. You can’t do protection updates, you can’t do a scan, you can check scans but once you exit out windows defender, it traditionally turns off periodic scanning.

Now, one of the three computers managed to download an update tonight and told me of a registry value had been found that is DisableAntiSpyware. Now, I checked all three computers where it told me to look (HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender) but none of the other computers have this registry line.

I am 98% certain the disableantispyware notification is a false positive in defender and it’s just due to norton closing it. IF it was malware, the malware would have shut off both. And across three computers that don’t run on the same wifi network?

Anyone else experiencing similar issues?

2

If the change in behaviour started just after updating Defender, it would seem to be something in Defender causing the issue. Have you restarted your computer after the updates? Restart, not shutdown and startup again.

3

All: I haven’t ever manually updated Defender with Norton installed but have depended on Windows Updates to provide the updates for it. From what I read here, I think manually updating Defender may be the core issue.

Relevant?

SA

4

Guys, I’m well aware that it is likely Windows Defender’s doing. But this situation does seem to stem from Norton and Windows Defender communicating with each other.

I’ve been using Norton since around 2008. I’ve known for years, around my third computer and Windows 10 that Norton shuts off Windows Defender. But at the same time, Windows Defender does allow periodic scanning where you can do a quick scan, full scan, offline scan and protection updates. I occasionally maybe once or twice a month run a protection update and run a quick scan and sometimes an offline scan.

I have three computers. Two laptops with 26H2 and one desktop with 23H2. They all have the latest version of Norton and its updates

September 22nd, 2026

On Laptop A, I decided to run a periodic scan. When I do a quick scan with Windows Defender, I often do a protection update pass first. My Windows Defender updated to 4.18.26080.4-0. As soon as the update finished, the quick scan would not start. I closed Windows Defender and went back in, where it says norton is protecting this computer flashed a few times when I pressed periodic scanning but it would open the Periodic Scanning section, for a few seconds. The scan would start then immediately stop seconds later and protection updates gives an error message. Basically everytime I log into periodic scanning, it stays open for a few seconds before closing. You can notice the Windows Defender EXEs in task manager pop up and disappear in a matter of seconds each time. Norton continued to run with no issues.

September 23rd, 2026 - Early AM

I updated both Laptop B and Desktop and both give me the same issue. As a test, I uninstalled Norton on one of the laptops to see if Windows Defender would work and instantly Windows Defender was working again and I was able to do scans and protection updates. But when I installed Norton back, once more Windows Defender periodic scanning only stayed open for a few seconds.

I want to stop right here for a second for those that say that’s normal. It’s not. I’m usually able to do peridoic scanning and do quick scans and protection updates with no problems FOR YEARS. This just started.

September 23rd, 2026 - Early PM

Investigated the cause of this. Read about a registry key in HKLM called - HKLM - Software - Policies - Microsoft Defender - DisableAntiSpyware. This registry apparently is often caused by third party antiviruses like Malwarebytes and Norton shutting down Windows Defender to be the default antiviruses as people have had issues to something similar I’m about to bring up. I checked all three devices to see if that key was on my computer and no, it did not exist in my registry on any of the computers

September 23’rd - Evening PM

On Latop B, when it was unplugged, I learned that Windows Defender closing was somehow stalled and it managed to get a protection update through. . . However, after the update finished, right inside protection history in Windows Defender I get an alert - that HKLM - Software- Policies - Microsoft - Windows Defender - Antispyware with the process of removal being abandoned. This is the very same registry key that I read about earlier and the same key that WAS NOT on all three computers. And when I researched this registry key, Malwarebytes forums talked about this very false positive before themselves about the registry key.

October 5th, 2026 - Early AM

Once again on Laptop B I got a periodic scanning to stay one slightly longer, long enough to download a protection update and once again got a second notice in protection history about that very same key.

A note about Laptop B. I barely use it and only do the Windows Updates on it. I keep it as a backup in case something happens. So I never visit weird or malicious sites or download on it.

Something has happened with Windows Defender after the version update with its communication with Norton It’s happend across THREE computers. And if you uninstall Norton, Windows Defender works perfectly so it’s not something malicious in the background, it’s how Norton and Defender communicate.