TL;DR: If you did a *new* installation of the previous Fedora Atomic Host, run:
ostree refs --delete fedora-atomic:fedora-atomic/25/x86_64/updates/docker-host This command will do nothing and be safe if you *aren't* affected. New installations as well as upgrades from older releases are not affected. A bit more information in: https://pagure.io/atomic-wg/issue/251 (However, if you want to participate in development, you'll likely be rebasing back/forth with the updates ref anyways, in which case there's no leak).
