Apple just released Security Update 2011-003 which can be downloaded and installed via Software Update preferences, or from Apple Downloads.
This is a small update weighing just 2.1 MB and requires Mac OS X 10.6.7 to install.
The OSX.MacDefender.A definition has been added to the malware check within File Quarantine.
The system will check daily for updates to the File Quarantine malware definition list. An opt-out capability is provided via the “Automatically update safe downloads list” checkbox in Security Preferences.
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.
If you’d like more information on how to remove Mac Defender, go here.