PRO DJ LINK transfers music files with an NFS server. In rekordbox this NFS server is started when you enable Link Export mode. On hardware like a CDJ-3000 or XDJ-AZ the NFS server is started when you boot up the player. The NFS server allows you to specify any file path. In rekordbox that means you can download any file on the hard drive. On hardware, it’s any file on your USB stick. On mobile devices, it’s any file that is inside the Secure Enclave. The NFS server has authentication but it’s a hardcoded value you add to the NFS header. There’s a patch for Rekordbox so download the latest version. A patch for Android and IOS apps is coming soon. Firmware updates for all-in-ones, and players are also coming. In the mean time, make sure you’re not putting important files in your USB stick, and only use PRO DJ LINK when you need it.