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.

Automatic action

Once the scan is complete, the F-Secure security product will ask if you want to uninstall the file, move it to the quarantine or keep it installed on your device.

Removal options

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.

Suspect a file is incorrectly detected (a False Positive)?

A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:

  • Check for the latest database updates

    First check if your F-Secure security program is using the latest detection database updates, then try scanning the file again.

  • Submit a sample

    After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.

    NOTE If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.

  • Exclude a file from further scanning

    If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.

    Note You need administrative rights to change the settings.

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Submit a sample

Submit a file or URL for further analysis.

Technical Details

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.

SLocker versions

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.