Both the Redhat and Fedora servers have been hacked by an attacker who has not only gained access to these systems, but may have also deployed rogue packages and signed them with Redhat's private key. Redhat has provided a script for users to check to see if the compromised packages have been deployed on their systems.

Security Advisory: https://rhn.redhat.com/errata/RHSA-2008-0855.html