I'm agreeing with Will here. However, I also know that Chrome OS is extremely hardened against viruses and rootkits, especially since the root partition cannot be written to easily. Not to mention that *all* apps reside in basically their own chroot jails, so the chances of a packaged app or something infecting the entire Cr-48, Chromebook or Chromebox are incredibly slim.
The only thing that probably will be of security concern is a
window-based JavaScript fork bomb, in that case a reboot is a quick fix. And probably an increase in phishing, but that can easily be fixed.