In response of the recent wave of MacDefender Trojan variants that have been tricking unsuspecting Mac users into installing malware, Apple has released a Security Update 2011-003 for Snow Leopard.

This security update enhances Snow Leopard’s XProtect feature, adding an “Automatically update safe downloads list” option to the Security system preference pane. This feature checks for new XProtect malware definitions daily, and automatically updates the definitions when they become available.