By US copyright law, all works are automatically put into copyright of the owner. Unless the creator explicitly licenses his or her material or retracts all copyright and puts it into the public domain, you have no rights to it.**
From a moral POV, the person may have released the source, but conventional courtesy dictates that you ask the creator beforehand, unless s/he provided a license with the file.
**Note: I am not positive if other countries have the same provisions. US copyright law tends to be a bit more "ahead," both in a positive and negative way. "Fair use," for example, is relatively unique to the US, I have heard.
I remember someone uploaded a map that was based off dye (though nothing like the original) to the map DB a few months ago, but I deleted it off because it was so hideously bad. I think this is that map.