bad breezy-security gpg signature?

Mon Feb 13 04:08:15 UTC 2006

Suddenly apt has been giving me the following error when I apt-get
update:

W: GPG error: http://security.ubuntu.com breezy-security Release: The
following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu
Archive Automatic Signing Key <ftpmaster at ubuntu.com> W: You may want
to run apt-get update to correct these problems

Everything has been running fine for months and I don't think I
changed anything lately. Apparently I have to apt-key add a new gpg
key, but I'm not sure where to get it from. Anyone know? 