How Do I Remove Or Uninstall Mac Defender?
The easiest way to remove Mac Defender is to download Security Update 2011-003. You can get it from that link or by going to your Apple menu and selecting Software Update.
If you are interested in manually removing Mac Defender, go to your Applications folder -> Utilities folder and launch Activity Monitor. Click on All Processes. Look for MacDefender (or MacSecurity / MacProtector) under the Process Name column. Once you have found it, click on it once and then click on Quit Process at the top left of the window. Then open your Applications folder, locate the Mac Defender application, drag it to your Trash, and empty the Trash.