Windows Security Virus Scan

Bree said:

Seems to be a bug in the current definitions, my tests show that Defender works fine with an older definition (1.313.1528.0) and crashes when updated to the current Security Intelligence update 1.313.1666.0 - but only when it scans a file with a 'double-dot' before the extension such as Filename..exe

I could recreate with filename..txt

[Restart now] button does nothing and requires a reboot.



I also noticed that I got a new Defender Platform last night 4.18.2004.5 after getting 4.18.2004.4 early AM Tuesday. Also the latest definitions didn't fix the issue 1.313.1668.0

stealth2920 said:

Guess I will wait until another update comes out to see what happens.

Steve C said:

Problem started after last security update as reported above.

I have been able to uninstall KB4549951 and go back to 18363.752. The Windows Defender Service still crashes when scanning a 'double-dot' file name, so that eliminates the latest CU as the cause. It seems the current security intelligence update is entirely to blame.

For those of you who have crashed their Defender service, the only way to restart it (besides a reboot) is from the Services app.

Also, before I ran this double-dot test I noticed, unlike before, I couldn't dismiss this [Set up OneDrive] nag until I rebooted.

Thanks Bree. Glad I didn't have to uninstall and reinstall that update even if I could have. Obviously must be the Security Intel update that messed up. Restarted in the services.msc for now

Steve C said:

... However, it stopped again after a couple of minutes!

Credit goes to @Pilovar who was the first to find this bug and had identified the crash as occurring when Defender scans any file with a double-dot before its extension. Without such a filename anywhere on my system that Defender regularly scans it does not stop for me.