Apple has released Security Update 2011-003 today with the express purpose of protecting Macs from the MacDefender malware. If the update is installed on a Mac that is already infected, the update will remove the malware program.
Available for: Mac OS X v10.6.7, Mac OS X Server v10.6.7
Impact: Remove the MacDefender malware if detected
Description: The installation process for this update will search for and remove known variants of the MacDefender malware. If a known variant was detected and removed, the user will be notified via an alert after the update is installed. Additional information is available in this Knowledge Base article:
Security Update 2011-003 is available now from the Software Update control panel or from the Apple Support Downloads page.