Well, sorry to necro this topic and sorry for not checking back for a long time, but here it is.
Avast Support recommended upgrading to a newer version of Avast, and that of course didn't change anything. In fact, the issue is still present with more recent builds of our software, with fresh and new installs of Avast (and various other common antivirus software). As always, virustotal says it's perfectly clean:
https://www.virustotal.com/en/file/f09b25555d8b37896fb692ff4b87faa5cd1cc91271de9902b1bb12253352db41/analysis/1510310305/All the files we ship in this thing (it's an ActiveState self-hosting executable, no installer, it just extracts various dlls and shipped files and executables during run) are also virus-free (and still more often than it's comfortable, they either get silently blocked from running, or silently quarantined; or when run separately also get sent for analysis and blocked, even though they had been run before from within the main software).
Eg.
https://www.virustotal.com/en/file/3f8bb63867ecf5f446cfefcf71a3d5db3fe604c32c0e99c1695336153dd9a75d/analysis/1510310847/Adding the directory that holds the shipped files to the white list doesn't help with the default settings of Avast, and we can't expect all our users to mess around with the antivirus settings.
Avast Support recommended using some Uninstall Tool I had never heard about to uninstall the old Avast and then install a new one — that was kinda strange, but whatever. Windows' built-in uninstall has always been sufficient.
I'm not sure what else we could do to not trigger heuristics simply due to our software not being used by millions of people.
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On my test system (a Windows 7), here's the current versions of Avast:
* Avast: 17.7.2314 (Build 17.7.3660.244)
* Virus definitions: 171110-0