My Avast forbids installation and reports:

THREAT: WIN32:CIH-G@dam

I would like an official comment about this, because it strongly looks like the files are really infected.

Reported files:

MAPPER.EXE
RAYRUN.EXE
CLIENT.EXE
STARTUP.EXE

I'm pretty sure it's false positive. Try to upload these files here - https://www.virustotal.com/

I did so, and the it confirmed the infection - see for yourself:

https://www.virustotal.com/en/file/e2df9355175033d19d5a6b1640da3c1a4b912bf2a56abf9c4d5e084ac23f3d31/analysis/

I am running scan on my computer now, and I will try to download and install on a separate computer, but please scan your files and if necessary, take action, since offering infected installers can have high impact indeed.

I will reboot the computer from an encrypted Linux partition, download the file again and have it rescanned by totalvirus web service to rule out the case that the file was infected immediately after download. It's unlikely, because I run an updated version of antivirus real time file checking at all times. Meanwhile, my scan of the system disk did not find any virus.

Meanwhile, I downloaded the file via plain http (no downloader), and scan confirms the files are infected.

Nah, I still think it's false positive. Also check this thread - http://www.gog.com/forum/rayman_series/some_exe_files_marked_as_viruses_probably_false_positives_but_still

The link you provided contains no proof of a false positive, just a statement backed by probably belief only.

Sorry, but this is not good enough.

Really? - http://www.gog.com/forum/rayman_series/some_exe_files_marked_as_viruses_probably_false_positives_but_still/post20

Yes, indeed. I see no proof in the link you provided, only a reassuring statement from GOG. By proof I mean a statement from at least one of the antivirus companies that developed the software that marked said executable as a virus.

That's at least 3 different results, with possibly 2 variants for CIH detection, from only 4 of the scanners. If it was an actual infection they should be same.

How long have you been a GOG member? This is a user forum. If you want an official comment send in a support ticket.

Sorry, but what you said just means that you trust Avast more than GOG, nothing else.

??? Then why are you posting here?

To raise awareness about the issue so that responsible people that care about their data and about other people on the internet, can exercise proper caution when installing software from GOG.
No, that just mean you do not understand the proper procedure on how these cases should be handled. Either the assessment of the antivirus software is a false positive, and then they should update their software not to raise it, because false alarms mislead their customers and lower the reputation of their software. Or the files indeed contain malicious code, and then GOG should not distribute it.

However, it's in the interest of both parties to clear the issue up to preserve their good reputation in the eyes of their customers. Therefore, GOG should have asked antivirus companies for explanation/evidence a long ago, and failing to obtain that (which I very much doubt would happen), issue a warning on the download page that certain product mark the files as infected but that to their best knowledge, they are not.

That would be a prudent and proper procedure on how to handle this issue.

To anyone concerned, I have received a statement from Avira regarding the suspicious file in the Rayman archive, You can read it here:

https://analysis.avira.com/en/status?uniqueid=QH9xHU2c9RmGhOMVwTyxrsOkXGTLP223&incidentid=1804837

That is the kind of information GOG should provide as an explanation to the concerned parties. I am still waiting for reports from the three other labs, but I presume they will arrive to a similar conclusion.

I use Avira. I don't know if it's internationally well-kown?

Please don't be that naiv.
On steam the game Portal 2: The Final Hours got also once hacked. Everything could be possible?
http://forums.steampowered.com/forums/showthread.php?t=2691619

I know, its a different topic, because this application is web based, but say never never!