Mac malware authors release a new, more dangerous version

Yesterday, 25 days after the Mac Defender malware began to appear in the wild, Apple finally responded. In a technical support note, “How to avoid or remove Mac Defender malware,” the company posted instructions for users to follow if they’ve encountered this malware specimen in the wild. It also promised a security update to remove infections automatically.

File that memo under, “Too little, too late.”

Within 12 hours of Apple’s announcement, the author of the original Mac Defender program had a new variant available that renders key portions of the current Mac Defender prevention plan obsolete.

A security researcher for Intego, the Mac-centric security company that identified the original Mac Defender, found the first example of this new code via a poisoned Google search very early this morning.

Several factors make this specimen different. For starters, it has a new name: MacGuard. That’s not surprising, given that the original program already had at least three names. But this one is divided into two separate parts.

The first part, a downloader program, installs in the user’s Applications folder. If you’re an administrator on your Mac (and most people are, given that the overwhelming majority of Macs have only one user and the default account in that scenario is an administrator), the installer will open automatically. All you have to do is click Continue to begin the installation.

Unlike the previous variants of this fake antivirus, no administrator’s password is required to install this program. Since any user with an administrator’s account – the default if there is just one user on a Mac – can install software in the Applications folder, a password is not needed. This package installs an application – the downloader – named avRunner, which then launches automatically. At the same time, the installation package deletes itself from the user’s Mac, so no traces of the original installer are left behind.

Update: The preceding scenario assumes that the user has visited the SEO-poisoned site using Safari (the default browser in OS X) and that the browser's default settings are in use. You can block the automatic installation in Safari by clicking File, Preferences, and then clearing the Open "Safe" Files After Downloading check box.

In this release, visiting a malware distribution site using Firefox or Safari causes a Zip file to be downloaded. Running the installer in that Zip file does not require an administrator password.

The downloader portion then installs the second part, which is similar to the original Mac Defender.

The new architecture seems to be a specific response to Apple’s instructions in the Mac Defender security note: “In some cases, your browser may automatically download and launch the installer for this malicious software. If this happens, cancel the installation process; do not enter your administrator password.”

In this new variation, no password is required as long as you're logged in using an administrator account. That might lull a potential victim into thinking they’re safe.

I know a lot of Apple users who breathed a sigh of relief yesterday, thinking that Apple’s belated response finally means that the problem is over. As any computer security researcher will tell you, this arms war is just getting started.

Apple appears to be treating this outbreak as if it were a single incident that won’t be repeated. They seriously underestimate the bad guys, who are not idiots. Peter James, an Intego spokeperson, told me his company's analysts were "impressed by the quality of the original version." The quick response to Apple's move suggests they are capable of churning out new releases at Internet speeds, adapting their software and their tactics as their target—Apple—tries to put up new roadblocks.

If Apple plans to play Whack-a-Mole with these guys, they’re in for months of misery. Just ask any Windows security expert who was around in 2003 and 2004 when Microsoft was learning a similar painful lesson. If each reaction from Apple takes two or three weeks, the bad guys will make a small fortune and Mac users can count on significant pain and anguish.

If you've run across this new variation in the wild, let me know. I'll have my eyes open and plan to report back if I find anything.