So, I got around to updating to the new Windows 10 Fall Creators Update (1709). Fine and well... for about 30 seconds. At that time, the updated Windows Defender saw fit to quarantine my PortableKeyboardLayout[edition DreymaR] claiming it was a trojan! Ugh.
The PKL_eD.exe file was marked as "Trojan: Win32/Azden.A!cl". Browsing the net, I found that this has often been a problem for people using compiled Autohotkey scripts, the executables being marked with various trojan tags by antivirus software. The description from Microsoft of this particular "trojan" was completely vague and generic.
I used the AHK v1.0.48 compiler (downloaded from the main AHK pages), as my code isn't quite ready for AHK v1.1+ yet. I've compiled these files from my source code and used them extensively without trouble for a long time now.
Oddly enough, the original PKL.exe (v0.4 preview) was not quarantined. But I'm quite confident it's a very false positive anyway. The original was compiled with AHK v1.0.47 I think.
To get back PKL functionality, I had to:
* Create an exclusion rule for the affected file in the Windows Defender Security Center → Virus & Threat Protection Settings.
* Under Scan History → Quarantined Threats, select the perceived threat and choose to Restore my file(s).
I hope Microsoft or the AHK community will fix this, but I'm in no way holding my breath. I've sent MS my file for analysis, together with some explanations.