Symantec warns of Android Trojans that mutate with every download

A new Android Trojan employs server-side polymorphism to generate unique variants

Researchers from security vendor Symantec have identified a new premium-rate SMS Android Trojan horse that modifies its code every time it gets downloaded in order to bypass antivirus detection.

This technique is known as server-side polymorphism and has already existed in the world of desktop malware for many years, but mobile malware creators have only now begun to adopt it.

A special mechanism that runs on the distribution server modifies certain parts of the Trojan in order to ensure that every malicious app that gets downloaded is unique. This is different from local polymorphism where the malware modifies its own code every time it gets executed.

Symantec has identified multiple variants of this Trojan horse, which it detects as Android.Opfake, and all of them are distributed from Russian websites. However, the malware contains instructions to automatically send SMS messages to premium-rate numbers from a large number of European and former Soviet Union countries.

In some cases, especially when security products rely heavily on static signatures, detecting malware threats that make use of server-side polymorphism can be difficult.

"As with malware that affects traditional computing devices, the level of sophistication of the polymorphism used can affect how easy or difficult the threat is to detect," said Vikram Thakur, the principal security response manager at Symantec. "More complicated polymorphism requires more intelligent countermeasures."

In the case of Android.Opfake the level of polymorphism is not very high, as only some of the Trojan's data files are being modified by the distribution server.

"If antivirus vendors place their detection on the executable and non-changing sections, all files would be successfully detected," said Tim Armstrong, malware researcher at Kaspersky Lab. However, if the Trojan's executable code were also polymorphic, the challenge of detecting it would be more difficult, he said.

According to Armstrong, server-side polymorphism is not very widespread on the Android platform at the moment because most users get their apps through official channels and the current structure of the Android Market does not allow for a malware distribution scheme like this one.

However, he agrees that polymorphic Android malware could force antivirus vendors to step up their game in the future. "I think many of the features that are currently available on traditional platforms will start to arrive on these mobile platforms out of necessity as the criminals change their attack methods," Armstrong said.

There have been many new developments on the mobile threat landscape recently and increasing their attention towards smartphones is a logical move for malware writers, because they usually go where the money is, said Jamz Yaneza, research manager at antivirus company Trend Micro.

Users should become more aware of this fact and the capabilities of their mobile devices, which are now similar to those of mobile PCs, Yaneza said. "They should treat app downloads with the same caution as they do on desktops," and install or make use of whatever security add-ons they can as this creates another protective layer.

Join the Good Gear Guide newsletter!

Error: Please check your email address.

Our Back to Business guide highlights the best products for you to boost your productivity at home, on the road, at the office, or in the classroom.

Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

Lucian Constantin

IDG News Service
Show Comments

Essentials

Microsoft L5V-00027 Sculpt Ergonomic Keyboard Desktop

Learn more >

Lexar® JumpDrive® S57 USB 3.0 flash drive

Learn more >

Mobile

Lexar® JumpDrive® S45 USB 3.0 flash drive 

Learn more >

Exec

HD Pan/Tilt Wi-Fi Camera with Night Vision NC450

Learn more >

Lexar® Professional 1800x microSDHC™/microSDXC™ UHS-II cards 

Learn more >

Lexar® JumpDrive® C20c USB Type-C flash drive 

Learn more >

Audio-Technica ATH-ANC70 Noise Cancelling Headphones

Learn more >

Budget

Back To Business Guide

Click for more ›

Most Popular Reviews

Latest News Articles

Resources

PCW Evaluation Team

Azadeh Williams

HP OfficeJet Pro 8730

A smarter way to print for busy small business owners, combining speedy printing with scanning and copying, making it easier to produce high quality documents and images at a touch of a button.

Andrew Grant

HP OfficeJet Pro 8730

I've had a multifunction printer in the office going on 10 years now. It was a neat bit of kit back in the day -- print, copy, scan, fax -- when printing over WiFi felt a bit like magic. It’s seen better days though and an upgrade’s well overdue. This HP OfficeJet Pro 8730 looks like it ticks all the same boxes: print, copy, scan, and fax. (Really? Does anyone fax anything any more? I guess it's good to know the facility’s there, just in case.) Printing over WiFi is more-or- less standard these days.

Ed Dawson

HP OfficeJet Pro 8730

As a freelance writer who is always on the go, I like my technology to be both efficient and effective so I can do my job well. The HP OfficeJet Pro 8730 Inkjet Printer ticks all the boxes in terms of form factor, performance and user interface.

Michael Hargreaves

Windows 10 for Business / Dell XPS 13

I’d happily recommend this touchscreen laptop and Windows 10 as a great way to get serious work done at a desk or on the road.

Aysha Strobbe

Windows 10 / HP Spectre x360

Ultimately, I think the Windows 10 environment is excellent for me as it caters for so many different uses. The inclusion of the Xbox app is also great for when you need some downtime too!

Mark Escubio

Windows 10 / Lenovo Yoga 910

For me, the Xbox Play Anywhere is a great new feature as it allows you to play your current Xbox games with higher resolutions and better graphics without forking out extra cash for another copy. Although available titles are still scarce, but I’m sure it will grow in time.

Featured Content

Latest Jobs

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?