Apple in a new support document kbht4650 announced that an update to Mac OS X will be issued in "the coming days" to squash the Mac Defender malware and its known variants. The update will also help protect users by providing an explicit warning if they download this malware.
In the meantime, Apple suggesting the following manual resolution for users affected with the malware:
How to avoid installing this malware
If any notifications about viruses or security software appear, quit Safari or any other browser that you are using. If a normal attempt at quitting the browser doesn't work, then Force Quit the browser.
In some cases, your browser may automatically download and launch the installer for this malicious software. If this happens, cancel the installation process; do not enter your administrator password. Delete the installer immediately using the steps below.
- Go into the Downloads folder or your preferred download location.
- Drag the installer to the Trash.
- Empty the Trash.
How to remove this malware
If the malware has been installed, we recommend the following actions:
- Do not provide your credit card information under any circumstances.
- Use the Removal Steps below.
- Move or close the Scan Window
- Go to the Utilities folder in the Applications folder and launch Activity Monitor
- Choose All Processes from the pop up menu in the upper right corner of the window
- Under the Process Name column, look for the name of the app and click to select it; common app names include: MacDefender, MacSecurity or MacProtector
- Click the Quit Process button in the upper left corner of the window and select Quit
- Quit Activity Monitor application
- Open the Applications folder
- Locate the app ex. MacDefender, MacSecurity, MacProtector or other name
- Drag to Trash, and empty Trash
Malware also installs a login item in your account in System Preferences. Removal of the login item is not necessary, but you can remove it by following the steps below.
- Open System Preferences, select Accounts, then Login Items
- Select the name of the app you removed in the steps above ex. MacDefender, MacSecurity, MacProtector
- Click the minus button
Use the steps in the "How to avoid installing this malware" section above to remove the installer from the download location.