After or during the update process for GOG Galaxy to 1.2.31 (update from the 7th of December 2017) Avast and AVG can detect some of the exe files are viruses or malware. This is a false positive, most likely caused by the new certificate we used to sign these files. We are working to solve this issue.
The current installer should no longer have this problem. If you are still encountering it please try the following:
Please open Avast, Click the Settings in the bottom left corner, click the Updates tab, here select to update the Software and Virus Definitions.
Please remove any Galaxy files put into quarantine by Avast, here is the list:
GOG Galaxy Notifications Renderer.exe
Delete the GalaxyClient.exe from the installation directory, default:
C:\Program Files (x86)\GOG Galaxy
Now restart your computer.
Download the latest installer from:
and try installing GOG Galaxy again.
Similar steps should work for AVG.