From The SANS Institute: (November 20 2007)

Security bug researchers (and others with more malicious purpose) have

been focusing on Apple OS X, and they have been very successful. Quoting

from the first item in this week's issue: "...several [OS X]

vulnerabilities are exploitable by remote users. Several file format

vulnerabilities are also present. Several implementation errors also

exist in the Mac OS X application firewall."

If you are ever asked which operating system is safer, the following

'non-aligned' rule may be of some help.  Given a fixed level of

programming skill, the number of vulnerabilities in software is directly

proportional to the number of lines of code and inversely proportional

to the length of time the software has been in wide use.  Large numbers

of critical vulnerabilities are being, and were bound to be, discovered

in Apple's operating system because Steve Jobs may design better

hardware, but his programmers are no better at writing secure code than

programmers in other software organizations.

                                    Alan