[HTCondor-users] avoid WARNING when using apt-get to install condor

["IJff, E.G." <bert.ijff@xxxxx>]

When I use
   apt-get install condor
on Ubuntu 12.04 I always get the message
WARNING: The following packages cannot be authenticated!
  condor

What should I do to get rid of this message,?
I.e. what should be done to successfully authenticate the package?

Best Regards,
Bert