Threat Descriptons



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Trojan-Spy:W32/Nuklus.A is a modular malware application mainly used for stealing online bank credentials.

It is installed to the system using a browser exploit. According to published reports, the links to sites containing the exploits were spammed.


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

System Installation

The trojan's main file, iexplore.exe, is downloaded via a browser exploit. When run, iexplore.exe drops the following files:

  • taskmang.exe The trojan's main executable.
  • mt_32.dll Configuration file containing the command and control server address.

It creates the following service:

  • ServiceName = "Taskmng" DisplayName = "Windows Task Manager" ImagePath = "%System32%\taskmang.exe"

It creates the following registry value:

  • [HKEY_CLASSES_ROOT\MTBase] = "%System32%\mt_32.dll"

The trojan injects itself to the web browser and runs the rest of the code in the context of the browser process.

After the installation, it contacts the server in the control file and starts to wait for commands. The remote server may instruct the trojan to execute any of the following actions:

  • Update the trojan's main file
  • Remove the trojan from the system
  • Download, activate, and remove additional components (plugins)


The remote server may instruct the trojan to download additional components using a plugin system. The plugin system consists of DLL files that are loaded by the main trojan or installed to the system using other methods, like browser helper objects (BHO) for Internet Explorer (IE). Plugins communicate with the control server using HTTP requests.

The following DLL files are basic plugins that may be installed to system:

  • CertGrabber.dll Collects certificates from the system certificate storage.
  • ExeLoader.dll Executes files.
  • FFGrabber.dll Mozilla FireFox HTTP request sniffer implemented as XML User Interface Language (XUL) extension module.
  • IECookieKiller.dll Removes cookies from the Internet Explorer cache.
  • IEFaker.dll Rewrite URLs. The fake addresses are controlled remotely by the attacker, this is reportedly used for phishing.
  • IEGrabber.dll IE HTTP request sniffer.
  • IEMod.dll Installs as a BHO and allows other modules to hook on internet connections.
  • IEScrGrabber.dll Capture IE screenshots.
  • IETanGrabber.dll Redirects internet connections.
  • NetLocker.dll Gets/sets a list of system Layered Service Providers (LSP).
  • ProxyMod.dll Starts HTTP and Socks proxies on a random port.
  • PSGrabber.dll Collects miscellaneous credientials from the system (email accounts, et cetera).

Other plugins can also be installed to infected system.

Command and Control system

The remote server reportedly hosts a sophisticated command and control system that the attacker can use to control infected systems via a web interface.

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