New Android Ransomware Changes Device’s PIN Lock

A new Android screening-locking malware targeting mainly users in the United States has been discovered by ESET researchers, who say this is the first ransomware to change a smartphone’s PIN security code.

Previously discovered Android LockScreen Trojans have achieved the screen-locking functionality through bringing a ransom window to the foreground in an infinite loop, while also implementing a series of defense mechanisms that would keep the device locked out. However, that approach made it rather easy to get rid of the malware and to unlock the device through the Android Debug Bridge (ADB) or by deactivating Admin rights and removing the Trojan in Safe Mode, ESET notes.

Called Android/Lockerpin.A, the newly discovered malware circumvents such removal options by preventing users from regaining access to their devices unless they have root access and a security solution installed. The Trojan can be removed via a factory reset, but that would also erase all of the user’s data.

After installation, the malware tries to achieve Device Administrator rights by tricking users into accepting the installation of an “Update patch.” During this so called update, users actually get through the process of activating the malware’s Device Administrator privileges that are hidden in the underlying window.

As soon as the user has clicked the “Continue” button, the Trojan can lock the device and can also set a new PIN code for the lock screen. Soon after, it prompts users to pay a $500 ransom by displaying a warning allegedly coming from the F.B.I., which informs users that their device is harboring forbidden pornographic material.

Although the device has been locked, users could uninstall Android/Lockerpin.A from Safe Mode or with the help of ADB, and could also reset the PIN, but that would not help them regain control of their devices. These actions would work only if users had root privileges.

“After having reset the PIN, however, neither the owner nor the attacker can unlock the device, because the PIN is generated randomly and not sent to the attacker. The only practical way to unlock is to reset to factory defaults,” ESET’s Lukas Stefanko explained in a blog post.

The malware uses an aggressive self-defense mechanism to recall the Device Admin privileges if the user tries to deactivate them. Moreover, when a removal is attempted, the Device Administrator window is overlaid with a bogus window that effectively reactivates the elevated privileges, Stefanko said.

Additional self-protection functions in the Trojan attempt to kill antivirus programs running on the device, and the Trojan also monitors com.android.settings to prevent standard uninstallation through the built in application manager.

The newly discovered Android/Lockerpin.A is not being distributed via Google Play, but through third party markets, warez forums, and torrents. It pretends to be an application for viewing adult videos and 75% of its targets are users in the United States, as attackers can make bigger profits in this market.

Mobile devices running Android are increasingly becoming the target of choice for cybercriminals hiding their malware behind seemingly legitimate applications, some of which can sneak into the official Google Play store. However, vulnerabilities in older versions of Android, such as the Stagefright security flaw, also endanger users and enterprises that are adopting the BOYD model.