From the Smells Like a Breach dept.:
The Fedora Infrastructure team is currently investigating an issue in the infrastructure systems. That process may result in service outages, for which we apologize in advance. We're still assessing the end-user impact of the situation, but as a precaution, we recommend you not download or update any additional packages on your Fedora systems.

We'll share updates as we develop more information.

fedora-devel-list