Technically, your song enjoys copyright protection once you’ve produced it on some medium. Practically, the best way to ensure your rights is to register it with the US Copyright office. This can be done online, but it’s one of the worst, clunky, user-UNfriendly websites I’ve come across – I actually couldn’t figure it out. Leagalzoom.com will also register your song, but they want an arm and leg to do it.
I’ve read where our DAW projects have some built-in protection because 1. the work is already on a medium, and 2. the files have an embedded date to them. I suppose that could be faked, however