A report from MacStories indicates that a new piece of malware is circulating to Mac users. It disguises itself as a virus scanning tool, reportedly automatically installs itself from certain web pages, and cannot easily be removed by dragging to the trash.
It’s unclear what the app actually does, but it is clear that it is thoroughly unrelated with the official MacDefender security software. The number of threads over on the Apple Support Communities forums seems to suggest that quite a few people are being hit with this.