I get sometimes this warning when executing the ping command:

"WARNING: kernel is not very fresh, upgrade is recommended."

I'm confused since the kernel is very new:

Code:
$> uname -a
Linux ubuntu 3.5.0-17-generic #28-Ubuntu SMP Tue Oct 9 19:32:08 UTC 2012 i686 i686 i686 GNU/Linux
What generates this warning?

Thanks,
PM