More than 55,000 Android devices worldwide have been infected with malware that security vendor Kaspersky this week described as virtually irremovable for most users.
Kaspersky first observed the xHelper Android Trojan malware being used in mass attacks last year. Months later, the malware remains as active as ever and continues to pose a threat to Android users everywhere, according to the vendor.
Like most Android malware, xHelper is being distributed under the guise of legitimate apps — in this case, as "cleaners" and "speed-up" apps for Android smartphones. xHelper is also being downloaded by malware that comes preinstalled on Android smartphones from some device manufacturers, Kaspersky said. Users typically most at risk of their devices becoming infected are those who download apps from unofficial, third-party Android application stores.
Once installed on a device, the malware collects unique device information, such as android_id, manufacturer, model, and other data useful for targeted advertising purposes, says Igor Golovin, security expert at Kaspersky.
"xHelper significantly reduces the performance of the device and constantly displays intrusive ads," Golovin says. "Our test device turned out to be practically unusable after infection."
Mobile malware is a growing concern for enterprise organizations, especially those that permit the use of unmanaged and personally owned smartphones and tablets for work. Though attacks against mobile devices have not quite materialized in the way security experts have predicted so far, many believe it is only a matter of time before threat actors start attacking smartphone and tablet users more heavily. Numerous mobile malware tools have surfaced in recent years, including banking Trojans, spyware, tracking software, and cryptominers.
Many believe that Android devices will pose a bigger risk to enterprise security than devices running iOS because of the sheer number of malware tools targeting Android.
What makes xHelper particularly dangerous is its ability to stay put on an infected device even if the user deletes the malware and restores the device to factory settings. Once the app is installed, it disappears and cannot be found either in the program menu or on the main screen of the device, Kaspersky said. The only place it appears is in the list of installed apps in the system settings.
The malware downloads multiple other malicious files, including one called "Triada" that enables root access to the infected device. The root access allows xHelper to install malware directly into the system partition that is mounted at device start-up, Kaspersky said.
Typically, the partition is mounted in read-only mode, but the Trojan uses its root privileges to mount it in write mode so malware programs can be installed there. All files copied to the phone are designated as "immutable," meaning they cannot be deleted even by a user with the requisite level of administrative privileges.
"This malware utilizes root access and installs additional malicious code deep into the system and its recovery mechanism," Golovin says.
Since the code is installed using root access, it cannot be removed without it. However, this access level is not normally available to users or applications on Android, Golovin notes. "Basically, this malware is protected after installation by the system itself and its security mechanisms," he says.
Detecting the malware is difficult as well because the Trojan downloads and decrypts its payloads one after another multiple times in a manner reminiscent of Russian Matryoshka nesting dolls, he says. Most of the devices on which xHelper has gained root access so far have been running Android versions 6 and 7 from Chinese manufacturers.
Kaspersky researchers have found xHelper impacting Android devices around the world. But users in some regions have been impacted more than other regions. The differences are likely due to the heavier use of devices with preinstalled malware from some manufacturers in certain countries, Golovin says.
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