MAC Defender Variant Can Infect Without Admin Password

A new variant of the Mac Defender has been found that does not require an administrative password to be installed.

Intego first discovered the MAC Defender fake antivirus, which targets Mac users via SEO poisoning attacks (web sites set up to take advantage of search engine optimization tricks to get malicious sites to appear at the top of search results). Since then, several variants have appeared: MacDefender, MacProtector and MacSecurity, all of which are the same application using different names. The goal of this fake antivirus software is to trick users into providing their credit card numbers to supposedly clean out infected files on their Macs.

Intego today discovered a new variant of this malware that functions slightly differently. It comes in two parts. The first part is a downloader, a tool that, after installation, downloads a payload from a web server. As with the Mac Defender malware variants, this installation package, called avSetup.pkg, is downloaded automatically when a user visits a specially crafted web site.


If Safari's "Open 'safe' files after downloading" option is checked, the package will open Apple's Installer, and the user will see a standard installation screen. If not, users may see the downloaded ZIP archive and double-click it out of curiosity, not remembering what they downloaded, then double-click the installation package. In either case, the Mac OS X Installer will launch.

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.

Apple has posted instructions on how to remove the malware and promises to update Mac OS X to automatically detect and remove it soon.

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