1. OpenBSD: By default, this is the most secure general purpose operating system out there. The proof in the pudding? The fact that it suffered only two remote attack vulnerabilities in the last decade serves as solid evidence of its stringent security and strict auditing policy. Moreover, OpenBSD lacks a large enough attack surface (care of running numerous web applications) for hackers to exploit.
2. Linux: Linux is a superior operating system. When customized it can be set up to extremely secure. Linux has an impressive vulnerability patching policy.
3. Windows Server 2008: Say what you will about a Microsoft operating system's security; at the very least, they know how to improve and they've gone through the very worst security threats that the Internet can dish out. This iteration of Windows Server has improved backup and recovery, user account control, web server (IIS) role, and server role security configuration.
4. Windows Server 2000: This operating system is so secure that it took nearly a decade before Microsoft can come up with a better one. This OS for network servers, notebook computers, and corporate workstations continues to get monthly security patches even after nine years since its release.
5. Windows Vista: Microsoft attempted to fix the security issues that has plagued Windows 95, 98, ME, and XP, but they ended up alienating consumers instead. The main complaints that people aimed against the polarizing OS—confusing security policies and the lack of backward compatibility with older applications—were actually security measures that were supposed to make Vista a lot more protected from breaches and hacker penetrations.
6. Windows Server 2003: The good news is that Windows Server 2003 is still a more secure OS than Windows XP. The bad news is that, security-wise, it's even worse than its earlier prototype, Windows Server 2000. Nevertheless, it features competent security improvements like default disabling of vulnerable services and a built-in firewall.
7. Windows XP: It became one of Microsoft's greatest and most long-running releases (mostly because of Vista's failure to connect to the general Windows-using consumer base). Tragically, it's also one of the most non-secure operating systems of all time as well.Because this OS runs a lot of network services by default and allows users to access full privileges by default, it also gets hacked and breached on a nigh-daily basis by default as well.
8. HP-UX 11i: Even though it's not one of the most commercially successful operating systems in the market today, this Unix-based Hewlett-Packard OS has been included in this list because of its superior security policies to several more popular operating systems (namely, Mac OS X, Solaris, and Linux).
9. Solaris: This Sun Microsystems Unix-OS variant is on the lower notches of this article's security hierarchy because it's not inherently security-focused. Because of certain business-related circumstances as well, most of the Solaris source code has already been published via the OpenSolaris project.
10. Mac OS X: This Apple-made OS handles user permissions better than, say Windows XP, but it still contains an indecent number of vulnerabilities and remote exploits in its systems. That, coupled with Apple's slow response to many of its security issues, has landed this operating system at the bottom of this list.
