Hi @ljoelm,
Set your downloads to Force Downloads or X-Accel-Redirect/X-Sendfile and enable the Download requires login setting in WooCommerce > Settings > Products > Downloadable products > Access restrictions**. This will prevent non logged in users from downloading files.

Image Link: https://cloudup.com/cEA6BhMqhjV
Below is the documentation for Digital Products which may also help.
https://docs.woocommerce.com/document/digital-downloadable-product-handling/
Thread Starter
LJoelM
(@ljoelm)
Great, thanks Stuart. I’ve also just discovered that because I uploaded the mp3 to the media folder instead of uploading via the product editor, the url wasn’t restricted. WooCommerce docs don’t seem to mention that.