Hi, I'm new to GOG. I came here to buy Gabriel Knight Sins of the Fathers on the recommendation of some friends. So, I just downloaded the setup file for this game. During the download everything else on my computer slowed down a lot. Then my Norton antivirus popped up a warning to the effect that the publisher was unknown and they could not vouch for the safety of the file.
Not meaning to cast aspersions on GOG, but I'm worried about running the setup. Can anyone tell me if they had a similar experience that turned out all right?

No need to worry. Norton only tells you that they don't know the publisher. The file is safe.