There is hardly any difference in security as far as all the standard distros of Linux go(Ubuntu, Debian, Fedora, Suse, RedHat, CentOS, Arch, Gentoo). And the kernel versions(2.6.30, 2.6.18, 2.6.31, 2.6.32, 2.6.33) are different from windows service packs and the individual security patches how?
Linux could be targeted just as easily... if it was WORTH targeting.