Be aware that Avast is also triggered by the extracted file M3.exe and considers it malware.
Therefore only delivering the extracts does not solve this problem, at least if you are using Avast.

M3.exe has a ratio of 11/57.

Yes, you are right: my Antivirus program (Avast) sees it as Win32:Malware-gen.
Do you know why this is?

By the way, excluding both the URL and the bin directory of MYST III from Avast makes it work.

I try to download myst3v122patch.exe from demos.residualvm.org (http://demos.residualvm.org/patches/myst3v122patch.exe) but get an error: The connection to the server was reset while the page was loading. All other Myst3 patches can be downloaded successfully. What is the problem with myst3v122patch...