[ Thanks to Hungry
Hacker for this link. ]
“As you all know that in august 2008 the Fedora servers were
compromised and the digital signature used to sign all Fedora
packages may have been compromised. The digital signature is used
to ensure that packages you install are authentic and not hacked or
modified in any way. As such you cannot upgrade your Fedora
installation you need to make a simple update before automatic
updates will accept packages signed by the new key.”