New Mac malware poses as PDF doc

But Trojan code is crude, can't yet connect to control server, say security firms

Security firms today warned Mac users of a new Trojan horse that masquerades as a PDF document.

The malware, which was spotted by U.K.-based Sophos and Finnish antivirus vendor F-Secure, uses a technique long practiced by Windows attackers.

"This malware may be attempting to copy the technique implemented by Windows malware, which opens a PDF file containing a '.pdf.exe' extension and an accompanying PDF icon," said F-Secure today.

That practice relies on what is called the "double extension" trick: adding the characters ".pdf" to the filename to disguise an executable file.

The Mac malware uses a two-step process, composed of a Trojan "dropper" utility that downloads a second element, a Trojan "backdoor" that then connects to a remote server controlled by the attacker, using that communications channel to send information gleaned from the infected Mac and receiving additional instructions from the hacker.

Because it doesn't exploit a vulnerability in Mac OS X -- or any other software -- the malware instead must dupe users into downloading and opening the seemingly-innocuous PDF document, which is actually an executable.

Once run, the dropper downloads the second-stage backdoor and opens a Chinese-language PDF. F-Secure said that the PDF was another sleight-of-hand trick: "[The dropper component] drops a PDF file in the /tmp folder, then opens it to distract the user from noticing any other activity occurring," the company said in a description of the attack.

Both Sophos and F-Secure noted that the malware doesn't work reliably, and currently can't connect to the command-and-control (C&C) server because the latter isn't fully functional.

Mac malware is typically crude in comparison with what targets Windows PCs.

Because the C&C server is not yet operational and since it found samples of the Trojans on VirusTotal -- a free service that runs malware against a host of antivirus engines -- F-Secure speculated that the malware is still in the testing phase.

Although Apple's Mac OS X includes a bare-bones antivirus detector, it has not been updated to detect the just-noticed Trojan dropper or backdoor. Checks of several Computerworld Macs running Lion, for instance, found that Apple last updated its detector on Aug. 9.

Mac users had their biggest malware scare earlier this year, when a series of fake security programs , dubbed "scareware," were aimed at them.

Several antivirus companies, including Sophos, F-Secure and Intego, offer security software for the Mac.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer , or subscribe to Gregg's RSS feed . His e-mail address is .

Read more about security in Computerworld's Security Topic Center.

Join the CSO newsletter!

Error: Please check your email address.

Tags sophosMac OSsecurityf-securesoftwareMalware and Vulnerabilitiesoperating systems

More about AppleF-SecureIntegoMacsMicrosoftSophosTopic

Show Comments

Featured Whitepapers

Editor's Recommendations

Solution Centres

Stories by Gregg Keizer

Latest Videos

  • 150x50

    CSO Webinar: Will your data protection strategy be enough when disaster strikes?

    Speakers: - Paul O’Connor, Engagement leader - Performance Audit Group, Victorian Auditor-General’s Office (VAGO) - Nigel Phair, Managing Director, Centre for Internet Safety - Joshua Stenhouse, Technical Evangelist, Zerto - Anthony Caruana, CSO MC & Moderator

    Play Video

  • 150x50

    CSO Webinar: The Human Factor - Your people are your biggest security weakness

    ​Speakers: David Lacey, Researcher and former CISO Royal Mail David Turner - Global Risk Management Expert Mark Guntrip - Group Manager, Email Protection, Proofpoint

    Play Video

  • 150x50

    CSO Webinar: Current ransomware defences are failing – but machine learning can drive a more proactive solution

    Speakers • Ty Miller, Director, Threat Intelligence • Mark Gregory, Leader, Network Engineering Research Group, RMIT • Jeff Lanza, Retired FBI Agent (USA) • Andy Solterbeck, VP Asia Pacific, Cylance • David Braue, CSO MC/Moderator What to expect: ​Hear from industry experts on the local and global ransomware threat landscape. Explore a new approach to dealing with ransomware using machine-learning techniques and by thinking about the problem in a fundamentally different way. Apply techniques for gathering insight into ransomware behaviour and find out what elements must go into a truly effective ransomware defence. Get a first-hand look at how ransomware actually works in practice, and how machine-learning techniques can pick up on its activities long before your employees do.

    Play Video

  • 150x50

    CSO Webinar: Get real about metadata to avoid a false sense of security

    Speakers: • Anthony Caruana – CSO MC and moderator • Ian Farquhar, Worldwide Virtual Security Team Lead, Gigamon • John Lindsay, Former CTO, iiNet • Skeeve Stevens, Futurist, Future Sumo • David Vaile - Vice chair of APF, Co-Convenor of the Cyberspace Law And Policy Community, UNSW Law Faculty This webinar covers: - A 101 on metadata - what it is and how to use it - Insight into a typical attack, what happens and what we would find when looking into the metadata - How to collect metadata, use this to detect attacks and get greater insight into how you can use this to protect your organisation - Learn how much raw data and metadata to retain and how long for - Get a reality check on how you're using your metadata and if this is enough to secure your organisation

    Play Video

  • 150x50

    CSO Webinar: How banking trojans work and how you can stop them

    CSO Webinar: How banking trojans work and how you can stop them Featuring: • John Baird, Director of Global Technology Production, Deutsche Bank • Samantha Macleod, GM Cyber Security, ME Bank • Sherrod DeGrippo, Director of Emerging Threats, Proofpoint (USA)

    Play Video

More videos

Blog Posts

Market Place