Mac Security Update 2011-003 has appeared in Software Update and is available for immediate download and installation.
According to KB article HT4657, the update provides a File Quarantine definition for the OSX.MacDefender.A malware and Mac OS X 10.6.7 will now automatically update the definitions on a daily basis.
The update will also search for and remove MacDefender and its known variants. If you prefer to defuse your malware manually, be sure to refer to our guide. The update will be available later directly from Apple Downloads, and we'll update this post with a direct link at that time.