Trojan:Android/Koler

Classification

Malware

Trojan

Android

Trojan:Android/Koler, Android.Trojan.Koler.A

Summary

Trojan:Android/Koler is an Android app being promoted as part of a ransomware scheme. On installation, the app displays a (fake) notice stating the device has been 'locked' and demanding payment.

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.

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

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Technical Details

Trojan:Android/Koler.A is reportedly a mobile-targeted extension of the Reveton ransomware network.

If a user browsing online on an Android device lands on a malicious webpage, they will be prompted to download an app. Unlike similar attacks against users browsing on a PC or Mac machine, download of the file is neither silent nor automatic; the user must confirm the download and manually install the app. To encourage download and installation, the app is promoted as providing access to adult materials.

On installation, the app sends the device' International Mobile Subscriber Identity (IMEI) number to a remote server. It then opens a browser page that displays a (fake) notice over the Home screen saying the device has been 'locked due to security violations and all files have been encrypted', or words to that effect.

The specific wording of the message varies depending on the user's geographical location. For example, users in Finland will see a Finnish-localized message, users in Sweden will see Swedish-language text and users in the UK or US will see English text.

The message also demands payment of a 'fine', supposedly to decrypt the files. The app does not actually encrypt files on the device, but does interfere with normal usage of the device by displaying the notice repeatedly until the 'fine' is paid.