Kernel related security fixes and upgrades are included in the kernel update that yum/yumex/etc offer.
Please note that once a kernel update is installed, you must reboot your machine and select (if not done by default) the newer kernel to boot from. (to change the default kernel edit as root: /etc/grub.conf, "info grub", put the cursor in Configuration and hit enter for more info)
Other packages may also have security updates and those particular packages need to be upgraded as well.
There is no need to reboot after any package update except the kernel.
Sometimes there is not even a need to reboot for kernel updates if the updates are only for particular kernel modules that can be removed temporally, updated and reloaded, but this is for more experienced users.
The good news is that Kernel updates are not too frequent, but readily available if a big security problem is found.
Last edited by jam-one; 10-22-2005 at 10:48 PM.