Android malware is following in the footsteps of Windows malware with attackers adopting some of the same distribution and monetization techniques despite the major differences between the platforms.
The latest development is a mass email spam campaign being used to distribute Android scareware -- applications that use scare tactics to trick users into paying for worthless services. Researchers from security vendor FireEye identified one such campaign that was launched on Sept. 6 and is still ongoing.
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The rogue emails use themes like failed package delivery notifications from USPS or electronic wedding invitations that have long been used in phishing emails to spread Windows malware.
The emails contain links that lead to websites serving an Android package (APK) file called LabelReader.apk. This APK installs a known Android scareware application called FakeDefender that masquerades as a commercial Android security product.
"The malware deceives users into paying for cleanup of other non-existent infections on their device," said Vinay Pidathala, a senior security researcher at FireEye, Tuesday in a blog post. "In addition to displaying fake messages of infection, the APK also has the functionality to intercept incoming and outgoing phone calls as well as messages."
Using emails to distribute Android malware is not a new technique, but it is not a common one either. Most Android malware is still distributed through third-party app stores or Google Play, when malicious apps escape Google's detection.
In April, security researchers discovered a targeted email attack targeting Uyghur activists that was used to distribute an Android Trojan program. Unlike that attack, this new spam campaign aims at wide distribution of the malware and is not targeting a specific group of users.
"Spammed malware for Android is becoming more and more popular with cyber-criminals, because they can target more devices at once," said Bogdan Botezatu, a senior e-threat analyst at antivirus vendor Bitdefender, Tuesday via email. "This is already the third wave of spam leading to Android malware this year and we presume that cyber-criminals are still just running tests to see how well their threats perform before taking the business to the next level."
According to security researchers, this trend is likely to intensify and is driven in part by the fact that a large number of people now check their email from their smartphones instead from their computers.
"As client-side antispam solutions for Android are scarce, chances are that spam will make it more easily into the users' mobile inboxes," Botezatu said.
Users forget that their mobile devices are not as well protected as their PCs, which usually have anti-malware, firewalls, disk encryption and other security products installed, said Jason Steer, a senior architect at FireEye, via email.
Furthermore, legitimate third-party app stores are getting better at identifying malicious apps and using email to distribute Android malware bypasses the app stores entirely, he said.
Another interesting aspect of this new spam campaign is that it targets multiple platforms. The links spammed in the rogue emails lead to some websites that check the User-Agent headers sent by users' browsers to determine their OSes. If a visiting user runs a Windows browser the website will serve a malicious .zip file containing Windows malware, but if they're using an Android browser it will serve the malicious Android APK.
"The first time we saw a platform-aware spam campaign that also involves Android was in March this year, when spamvertised links would redirect users to either infected APKs or to a Blackhole exploit kit," Botezatu said. "This way, every single potential victim is carefully profiled for flaws and redirected to the appropriate infection mechanism. This technique could either hint that cyber-criminals who deal with Windows malware are expanding their business to other platforms, or that they are actually leasing their infrastructure to cyber-criminals with a particular focus on Android."
"More and more threats are multi-browser and multi-OS enabled, ensuring maximum coverage on user endpoints and maximum distribution," Steer said.
Like Android threats distributed from third-party app stores, the Android scareware distributed through this spam campaign can only affect devices configured to allow the installation of apps from sources other than Google Play. This is a setting that comes disabled by default in Android, but many users turn it on, primarily because they want to install legitimate apps that are not available on Google Play or because they don't have Google Play access.
"I'd say that there are plenty of users out there who allow installation of applications outside the official channel," Botezatu said. "Although I can't speculate on numbers, there is a huge pool of Android adopters in Asia, for instance, who can't fully take advantage of Google Play, so they have to rely on third-party markets to buy apps."
Most users are not security conscious and are unaware of the implications of turning this feature on, Steer said.