Linux is more secure than Windows, but I don’t think it is as secure as Solaris (don’t know about OpenSolaris) or the BSDs. Now, that said, SOME Linux are as secure, such as Bastille or Monta Vista, security is their prime focus. I would suggest Debian Stable is more secure than Ubuntu 8.04 (simply because the new functions are not as vetted, not a slam).
Now, the most secure OS ever, Knoppix (or any CD based distro). It CAN”T be infected or 0wned, ever, even if full of security holes, next reboot, it is pristine.
I think Apple has sacrificed BSD security for convenience, making it not as secure (the number of critical updates seems to bear this out), and still include Quicktime, the mandatory security exploit propagation application (I hear it plays music too!)
Windows, however, still brings up the bottom. Vista is better with non-admin, but that’s about it, and it still supports Active-X, so can never be secure.
TripleII