A significant new security threat has been detected and its putting Mac users on high alert today. Mac antivirus and security developer Intego has "discovered a rogue anti-malware program" dubbed MACDefender. According to a report from the agency, MACDefender attacks Macs via "SEO poisoning" assaults. (NOTE: The malware described here is in NO WAY affiliated with MacDefender, makers of popular geocaching software).
This latest security threat represents yet another example of how malware sites are capitalizing on Safari's "Open Safe Files" feature. Nonetheless, if you have installed the MACDefender software, there's a good chance you'll be able to uninstall the unwanted "house guest" in just a few steps - the first of which is searching for and deleting any and all references to "MACDefender" on your system.
According to CNET:
Currently antivirus definitions for Intego's VirusBarrier X6 software are being updated to address this threat, and it is likely other legitimate antivirus software companies are doing the same for their programs. Therefore, if you run VirusBarrier or other antivirus utilities then be sure to check for an update soon, and run a full scan on your system to remove the MACDefender malware.