Hmm… looks like Avast gives a false positive on this game (Fate of the World). It quarantines the game thus rendering it unplayable - but other virus programs do not seem to notice anything amiss?
So, I wonder - is it safe to dismiss that warning now? ???
Seems there does not exist any release that is completely virus free,
Keep in mind that a game crack will often come up as a false-positive with antivirus scanners or malware detectors and there is a reason for that…
polonus
Submit the file to www.virustotal.com and check 
It is an original, non-modified Steam game, though. : Furthermore, I never use any game cracks or hacks. But whenever I try to download that game from Steam, it stops fast because of the download triggers Avast control.
Ah well, I shall do what Tech suggested - I have to check if it finishes download ( so I can submit it to virustotal) at all since it is quarantined so fast.
BTW: I am not the only one having this problem as others in Steam game forums have also discussed that , and all have Avast. So either Avast is the best and only one to note the trouble - or then it fails here.
Pause the web shield when downloading it or it will stop the download completing, don’t forget to enable it again. The file system shield may throw it in the chest but at least you have a copy.
You could also check the offending/suspect file at: VirusTotal - Multi engine on-line virus scanner and report the findings here the URL in the Address bar of the VT results page. You can’t do this with the file securely in the chest, you need to extract it to a temporary (not original) location first, see below.
Create a folder called Suspect in the [b]C:[/b] drive. Now exclude that folder in the File System Shield, Expert Settings, Exclusions, Add, type (or copy and paste) C:\Suspect*
That will stop the File System Shield scanning any file you put in that folder.
Hmm… Before I got around to do this, it seems that the problem has been corrected. Either due to 2 updates by Fate of the World creators or some Avast updates. Probably the previous - so ithe game now reports to be clean. Dunno what gave that alarm out in the first place though.
But good to know the procedure in case another Steam game starts behaving like that! 