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An article at ZDNet Australia advises that Mac OS X continues to be the safest option compared to Windows XP or its successor Windows Vista.
They refer to the Security Threat Management Report 2006 (pdf) by Sophos, which highlights the fact that only one piece of malware targeting OS X has been found in the wild — and even that has not really posed a threat.
This compares to 40,000 pieces of malware that have been discovered for Microsoft’s Windows operating system in the past year alone.