Mac Defender

From Penn Information Systems and Computing:

Information is trickling in from both on and off campus about the distribution of fake security software targeted directly at the Macintosh desktop OS. The program, MAC Defender, is similar to existing "rogueware" which has existed on the MS Windows platform for a while.
The app claims that the Mac is heavily infected with malware. An unsolicited install dialog box appears prompting the user to type in an administrator password.

Once installed, software alerts users with pervasive pop-ups indicating that their system is infected and that only the "full" program will remove the threats. The full program, of course, is easily downloaded once the user types in a valid credit card number.

Symantec's response, including Antivirus Protection Dates (pending):

http://www.symantec.com/business/security_response/writeup.jsp?docid=2011-050313-0713-99

Additional information from Intego:

http://blog.intego.com/2011/05/02/intego-security-memo-macdefender-fake-antivirus/

Please let us know if you are seeing the above behavior. We'll share any additional information that we receive about this threat.