Threat Descriptons



Category :


Type :


Aliases :

JS.Nemucod.[variant].Gen, Generic.JS.Nemucod[variant], Generic.JS.NemucodA.[variant], Js:trojan.downloader.nemucod.[variant], JS:Trojan.Downloader.Nemucod.[variant], Trojan.JS.Downloader.Nemucod.[variant], Trojan-Downloader:JS/Nemucod.[variant]


Trojan-Downloader.JS.Nemucod downloads and runs additional malicious files onto the system. The downloaded files are typically info-stealers, though in more recent campaigns Nemucod has also been seen delivering ransomware.


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.Nemucod is distributed as a JavaScript file embedded in a ZIP file that is attached to an email message.

The emails used to deliver Nemucod are typically spam, sent out to recipients in mass mailings by the malware's distributors. The emails are usually social-engineered to appear legitimate or enticing.

Downloads malware

If an unsuspecting recipient opens the attached ZIP file and runs the JavaScript file it contains, Trojan-Downloader.JS.Nemucod will download a file to the %TEMP% folder and run it.

Nemucod is usually used by attackers to distribute malware such as Zeus variants or various password- or info-stealers. In more recent malware distribution campaigns, the file observed being downloaded by Nemucod has been ransomware, typically either TeslaCrypt or Locky.

Nemucod may also open a separate document as a decoy to mislead the user.

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