If you don't trust mediafire, yet alone the installer. You won't be able to play the maps.
If you press the download link for the installer and nothing else there wont be any infections or threats what so ever.
Norton gives out too many false threats, and if you want to install the map pack, you have to ignore the threat via norton if possible, or shutting it off during the download and install progress.
As mentioned earlier, the installer files are 100% from me and my computer, and it was scanned with AVG and Avast before I put it up. There's no threats if you just click the download link.