I do not know why Norton thinks its a trojan based on the information provided, however it is suggested that you temporarily disable any virus protection software while attempting to download these files.
This post should explain how to install the latest version of KGCM:
Installation instructions for v4.2
If you are only interested in v3.0 then refer to the corresponding installation instructions for that version which will require the fixes. However I believe that 4.2 is a much better version of the game. If you are satisfied with it, you may want to consider Heroes, Hordes and Beyond sub-mod which continues to build on the KGCM while retaining the same feel and playability.