Trojan:Android/SLocker.A is reportedly the first Android ransomware that uses file encryption. It is also noted for its use of the TOR anonymizing network to communicate with its controller.
Trojan:Android/SLocker disables the Back button when displaying the ransom message to block the user from trying to recover normal use of the device. The user may however have a few seconds to remove the malicious app by pressing the Home button and dragging the app to the top of the screen to uninstall it.
Alternatively, the user may elect to perform a factory data reset on the device to remove the malicious app. This will also erase all user files saved to the device's main memory, but will not affected files stored on an external memory card.
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On installation on a device, SLocker scans the device for image, document and video files and encrypts them using the AES encryption algorithm. The malware then displays a ransom message to the user, demanding payment to provide the decryption key necessary to unencrypt the affected files.
Similar to the Trojan:Android/Koler ransomware (which pretends to but does not actually encrypt files on the device), the Back button is disabled when the ransom message is displayed.
There are currently two versions of SLocker. The most notable version communicates through TOR in order to receive commands. This version is able to collect sensitive information from the device such as its International Mobile Equipment Identity (IMEI) number and return the information to the Command and Control (C&C) server that issues its commands.
The second SLocker version receives commands through SMS messages. Commands have been observed originating from phone numbers traced to Ukraine and Russia.
Both versions of SLocker use the same code (including the same AES password) for decrypting the files held at ransom.