I opened Galaxy some time ago and FEAR 2 got a 27MB update. 26 actually, really, though, as my antivirus got a warning and disinfected a file. In the report, i saw the route: temp/1449651388/sourceserver.exe.download

and then: Virus: Gen.variant.strictor98156

What on earth is this files and why the hell FEAR 2 got NOW an update?

Also now, the "Play" button for FEAR 2 in my galaxy client shelf became un-clickable. For the love of god, what is happening here?

the end is near!

Repent, you sinners!

I wouldn't know for sure, but it's probably a false positive. Looking up the name of the "virus", I only find two mentions of it elsewhere: A Steam forum thread asking about it from a game update (I don't think the game was specified) and again on the official Grim Dawn forums. Again, I don't know for sure that it's safe, but don't get too freaked out just yet.

False positive?

Get a better antivirus.

Probably, I got the same when I installed Ziggurat and a few other games from GOG Galaxy. I agree, it is better to make sure it's safe.

My suggestion, install the game without GOG Galaxy, and then add it to the local library.

Edit: Or, use the rollback feature.

Anti virus programs use virus signatures and heuristic analysis.

The signature is like a detailed description of any given virus. Like a photo of a Great Dane, poodles and different types of Dog.

Heuristics look at all the photos and weighs the chances of this unknown photo is a dog.

A False Positive is when it looks at a picture of a Shaggy cat and marks it as a Dog.

Worse is a False Negative, Where is looks at a dog that's been painted yellow and marks it as "Not Dog".

AHK (AutoHotKeys) often gets mistaken for a virus as well. True it contains everything you'd need to build your own virus, including accessing/reading keyboard strokes, direct control over hardware, accessing the drive, writing and reading files, changing permissions and dates, etc. But just because functions are present doesn't mean it's a virus. (although AHK also throws many anti-cheat programs)

Don't F.E.A.R. It is probably a polse fasitive (providing you are using the official Galaxy client downloaded from GOG, not some unofficial version downloaded elsewhere). FEAR 2 doesn't have a changelog and I didn't see it mentioned recently in the "what has been updated" thread, so I presume the update you got is something related to the Galaxy version only, not the game itself.