Mac trojan evades Apple's brand new security fix
Welcome to the mass market, Cupertino
Just hours after Apple issued a security update to protect Mac users against a rash of scareware attacks , a new variant began circulating that completely bypasses the malware-blocking measure.
The trojan arrives in a file called mdinstall.pkg and installs MacGuard, a malicious application that masquerades as security software the user needs to clean a Mac of some nasty infections said to be discovered during a recent hard drive scan. As reported repeatedly  during recent days , a series of clever social engineering attacks on Google, Facebook and elsewhere have been besieging Mac users and tricking a fair percentage of them into installing the rogue antivirus packages.
On Tuesday, Apple updated OS X to detect MacDefender and its variants before users can install it, in what many are regarding as an admission by Cupertino that Mac fans, like users of Windows, need help keeping their machines free of malware. Underscoring that point, the purveyors of the Mac trojans responded, less than eight hours later, with the release of the latest MacGuard variant.
As ZDNet blogger Ed Bott pointed out , it “has been specifically formulated to skate past” Apple's just-released security update.
It's precisely the kind of cat-and-mouse fight that security companies and Windows malware purveyors have been waging for years. And now, it's coming to the Mac.
Now that Macs by default will update a list of known malicious applications every 24 hours, Apple has the ability to respond in kind. It will be interesting to see how long it takes for OS X to block the new variant. ®