Copyright is pretty much useless these days is it not? You could be Prince, Metallica or Avicii and have your music downloaded, copied, ripped, reworked, mixed etc etc without any kind of action taken for the most part. Some home made tunes by amatuers or unknown people being "protected" is nothing more than words on paper. It means nothing at all to anyone.
If people does not want anyone to mess with their music, there is only one solution and that is to not let anyone hear it in the first place. Making money on music is totally impossible today unless you are in the top tier so not sure what the copyright really provides to begin with for the common man.
Better approach is to appreciate someone liking it enough to mess with it creating new versions. Might increase the nr of people hearing it even, if that is why you put it out there I mean. That is about as much you can ever expect to get from posting your music online. Trying to fight the reality of things is rather futile.
If you dont think you have written the next nr 1 on Billboard, worrying about copyrights etc is a waste of time and resources. That is just my very humble opinion of course :)