Actually I don't know of any viruses that attack any Warcraft-based-filetype. Tools are checked by an anti-virus-prog before uploaded here, dunno if other resources are checked, too. Usually I download almost every map to test it, and I never saw any viruses or anything equal.
If the zip-archive is corrupted, most times the reason is that something interupted the download so parts of the files are missing. Try using a download manager, and winzip/winrar to open the archives.
Somehow it seems like you said you double-click on the map-files (-> starting them). If you do so, WC3 won't start them, it will just open WorldEditor. If the map is protected, you'll get that error you showed. Just extract them to your Warcraft3-maps-folder and play them in WC3 using "Singleplayer -> Custom Maps -> [where you extracted them]".