From everything I've read on Apple's discussion forums, the Mac Defender trojan/virus can only be installed on your Mac OS X system under the following circumstances:
From what I've read on the Apple discussion forums, here's how you delete the Mac Defender trojan from your system.
It looks like reports of the "Mac Defender" trojan/virus/malware are the real deal. Several Apple discussion forums related to the Mac Defender trojan (it's not a virus) have several thousands page-views and hundreds of comments. You can find these threads by searching Google with this query:
Mac antivirus software FAQ: What Mac antivirus software should I use? (Also written as, "Do I need Mac anti-virus software?" or "Should I use any Mac antivirus software at all?")
Hmm, it looks like there might be more than one reason for Apple retiring their famous Mac/PC commercials -- turns out they've quietly gotten into the malware/antivirus business.
MacWorld reports that Apple has quietly snuck an anti-malware (antivirus) update into the latest round of Mac OS X Snow Leopard updates. An antivirus program was included in Snow Leopard, and last week's Snow Leopard update included an update to the Mac OS X antivirus definition file (a simple Mac OS X plist file).
AppleInsider is reporting that Snow Leopard will include an "anti-malware" feature. Here's a brief excerpt from their story:
"In a screenshot that has been widely circulated, originating from the intego Mac Security Blog, Snow Leopard is shown to recommend that a .DMG file be moved to the trash. The OS claims that the file includes 'OSX.RSPlug.A' malware."