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Discovered: August 27, 2012
Updated: August 29, 2012 1:54:11 PM
Type: Trojan
Systems Affected: Windows
CVE References: CVE-2011-3544 | CVE-2012-0507

Trojan.Shylock.B is a Trojan horse that opens a back door on the compromised computer and attempts to steal potentially confidential information. It may also attempt to spread.

For more information, please see the following resource:
The Shylock “LNK” Awakening

Antivirus Protection Dates

  • Initial Rapid Release version August 27, 2012 revision 009
  • Latest Rapid Release version November 04, 2019 revision 019
  • Initial Daily Certified version August 27, 2012 revision 016
  • Latest Daily Certified version November 04, 2019 revision 065
  • Initial Weekly Certified release date August 29, 2012

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Technical Description

This threat is known to arrive on the compromised computer by exploiting the following vulnerabilities:
Oracle Java SE Rhino Script Engine Remote Code Execution Vulnerability (CVE-2011-3544)
Oracle Java SE Remote Java Runtime Environment Code Execution Vulnerability (CVE-2012-0507)

When the Trojan is executed, it creates the following file:
%Temp%\[ONE LETTER].tmp.exe

It then opens a back door and connects to the command-and-control (C&C) server in order to download additional component files.

Next, the Trojan gathers information about the compromised computer and sends it to the C&C server.

It also injects itself into a svchost.exe process in order to receive commands from the C&C server. Some of the commands it can perform are as follows:

  • Uninstall itself
  • Setup a Virtual Network Computing (VNC) session
  • Gather cookies
  • Execute a file
  • Upload a file
  • Spread itself

It may attempt to spread by replacing the following file types on removable drives and network shares:
  • .ma
  • .md
  • .acc
  • .ad
  • .vtx
  • .vsx
  • .vdx
  • .vst
  • .vss
  • .vsd
  • .ppsx
  • .pps
  • .pptx
  • .ppt
  • .one
  • .docx
  • .doc
  • .xls
  • .lnk
  • .bat
  • .com
  • .exe

When one of the extensions listed above is found, it renames the original file as the following name:

It sets the attributes of this file to Hidden and System so the file is hidden from the user when exploring folder content in Explorer.

Next, the Trojan creates a copy of itself in the same directory and names it thumbs.dbh.

It also creates the following file as a replacement for the original file in order to trick users into running the Trojan:

The Trojan then runs itself and also opens the original file in order to avoid suspicion from the user.


Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.


You may have arrived at this page either because you have been alerted by your Symantec product about this risk, or you are concerned that your computer has been affected by this risk.

Before proceeding further we recommend that you run a full system scan . If that does not resolve the problem you can try one of the options available below.

If you are a Norton product user, we recommend you try the following resources to remove this risk.

Removal Tool

If you have an infected Windows system file, you may need to replace it using the Windows installation CD .

How to reduce the risk of infection
The following resources provide further information and best practices to help reduce the risk of infection.

If you are a Symantec business product user, we recommend you try the following resources to remove this risk.

Identifying and submitting suspect files
Submitting suspicious files to Symantec allows us to ensure that our protection capabilities keep up with the ever-changing threat landscape. Submitted files are analyzed by Symantec Security Response and, where necessary, updated definitions are immediately distributed through LiveUpdate™ to all Symantec end points. This ensures that other computers nearby are protected from attack. The following resources may help in identifying suspicious files for submission to Symantec.

Removal Tool

If you have an infected Windows system file, you may need to replace it using the Windows installation CD .

How to reduce the risk of infection
The following resource provides further information and best practices to help reduce the risk of infection.
Protecting your business network

The following instructions pertain to all current Symantec antivirus products.

1. Performing a full system scan
How to run a full system scan using your Symantec product

2. Restoring settings in the registry
Many risks make modifications to the registry, which could impact the functionality or performance of the compromised computer. While many of these modifications can be restored through various Windows components, it may be necessary to edit the registry. See in the Technical Details of this writeup for information about which registry keys were created or modified. Delete registry subkeys and entries created by the risk and return all modified registry entries to their previous values.

Writeup By: Branko Spasojevic