Threat Descriptions

Trojan-Downloader:JS/Downloader.IOK

Classification

Category :

Malware

Type :

Trojan-Downloader

Platform :

W32

Aliases :

Downloader

Summary

Trojan-Downloader:JS/Downloader.IOK is a JavaScript file that silently downloads and executes other files onto the affected machine.

Removal

Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.

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 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.

Technical Details

Trojan-Downloader:JS/Downloader.IOK is distributed as a file attached to an email message. In the sample analyzed (SHA1: 9c4c9b5c9c0a67c9cec7398a0c47b37df8d92bd1), the email message used the title "My resume" while the attached file used the filename "re: Freddie Byrd.js".

The JavaScript file is obfuscated, making it impossible for the normal user to read the contents. If the user opens the attachment, the JavaScript launches and attempts to contact a remote server, which begins to silently download and execute other files on the affected machine.

Obfuscated JavaScript file

In the sample analyzed, the files downloaded were named "onewindows1s.jpg" and "twowindows2s.jpg". Despite the file names, which are indicative of image files, they are in reality executable programs.

Files downloaded by Trojan-Downloader:JS/Downloader.IOK

At the time of writing, these URLs are no longer accessible. Further analysis showed that the downloaded files were variants from the CryptoWall ransomware and Fareit password-stealing trojan families; both downloaded files are identified by generic detections.