If you don’t already know, Win32:Delf-MZG false positive was fixed in the latest VPS - 091203-1.
This should never mess your system if you choose move to chest and investigate, not delete as you have no options left. Or if you have had that file on your system for some time and all of a sudden it is now detected, yes it could have become infected, or was previously undetected, or a new signature is added or modified and it could be a false positive.
False positives in security applications are almost a fact of life and sooner or later you may get one; so you always need to air on the side of caution when dealing with infections, never delete, move to the chest and investigate.
That way if it proves to be a false positive you can restore it from the chest.