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Discovered: December 17, 2007
Updated: January 08, 2008 12:54:17 PM
Also Known As: [McAfee]
Type: Trojan
Infection Length: 54,189 bytes and 98,304 bytes
Systems Affected: Windows

Trojan.Silentbanker is a Trojan horse that records keystrokes, captures screen images, and steals confidential financial information to send to the remote attacker.

Antivirus Protection Dates

  • Initial Rapid Release version December 17, 2007 revision 023
  • Latest Rapid Release version November 04, 2019 revision 019
  • Initial Daily Certified version December 17, 2007 revision 032
  • Latest Daily Certified version November 04, 2019 revision 065
  • Initial Weekly Certified release date December 19, 2007

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

Technical Description

The Trojan may be downloaded or delivered silently through Web exploits and then executed. It arrives as the following file:

It then drops a dll file with the following file name pattern and then deletes itself:

At the time of writing, the following file names have been observed:

  • appmgmt14.dll
  • dbgen47.dll
  • drmsto34.dll
  • faultre66.dll
  • kbddiv55.dll
  • kbddiv79.dll
  • msisi83.dll
  • msvcp793.dll
  • msvcr25.dll
  • nweven2.dll
  • pngfil51.dll
  • pschdpr89.dll
  • versio40.dll
  • wifema85.dll
  • winstr21.dll
  • wzcsv64.dll

The Trojan drops additional randomly named files in the %System% folder to hold configuration information and to log information.

The Trojan also creates the following file which contains a list of all other file names that the threat uses:

It creates the following registry entry so that it runs when an application calls for a sound device:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Drivers32\"midi1" = "[RANDOM CHARACTERS][RANDOM DIGITS].dll"

Note: This may have the side effect of disabling your sound device.

The Trojan may also add itself as a Browser Helper Object (BHO) in Internet Explorer by creating the following registry subkey:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Browser Helper Objects\{[RANDOM CLSID]}

It also creates the following registry entries:

The Trojan targets many different banks using various methods in order to perform the following:
  • Gain access to accounts
  • Divert transactions to attacker controlled accounts

The Trojan performs the following actions:
  • Redirects legitimate requests to attacker controlled computers
  • Alters the HTML of pages shown to the user
  • Alters requests sent by the user to the bank
  • Captures screen shots of Web sites where the user must click instead of type the password
  • Sends full pages received by the victim to the attacker
  • Downloads new versions of itself
  • Downloads new configuration files
  • Records user names and passwords
  • Records the content of the clipboard
  • Steals cookies, digital certificates, and Adobe .sol files
  • Sends a list of all software installed on the compromised computer to the attackers

The threat hooks APIs in the following browsers:
  • Internet Explorer
  • Firefox

It may also hook APIs to the following file:

The Trojan hooks the following APIs in order to intercept traffic received to and sent by the browser:
  • Send
  • Connect
  • CryptDeriveKey
  • CryptImportKey
  • CryptGenKey
  • HttpOpenRequestW
  • InternetReadFileExA
  • InternetReadFileExW
  • CommitUrlCacheEntryA
  • InternetReadFile
  • InternetQueryDataAvailable
  • HttpOpenRequestA
  • HttpSendRequestA
  • HttpSendRequestW
  • GetClipboardData
  • DispatchMessageA
  • DispatchMessageW
  • ExitProcess

Next, it downloads compressed and encrypted configuration files from the Trojan’s control server. These configuration files contain the following information:
  • URLs to change the HTML
  • HTML to find on targeted pages
  • HTML to be inserted/deleted/replaced on targeted pages
  • URLs to redirect to attacker sites
  • URLs to target for stealing account information
  • URLs to take screen shots from
  • Keywords to search for
  • Domain names to monitor and send to the attacker
  • Location of control servers
  • Location of updated Trojan executable
  • Location to send all stolen data
  • Porn URLs
  • Various other configuration data

The Trojan creates the following mutex so only one instance of the threat is running:

The Trojan may attempt to access the following Web sites:

It may change the users DNS settings to the following attacker settings:

The Trojan then sends the collected information to the following remote locations:


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.


The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

  1. Disable System Restore (Windows Me/XP).
  2. Update the virus definitions.
  3. Run a full system scan.
  4. Delete any values added to the registry.

For specific details on each of these steps, read the following instructions.

1. To disable System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:

Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, reenable System Restore by following the instructions in the aforementioned documents.

For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article: Antivirus Tools Cannot Clean Infected Files in the _Restore Folder (Article ID: Q263455).

2. To update the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:
  • Running LiveUpdate, which is the easiest way to obtain virus definitions.

    If you use Norton AntiVirus 2006, Symantec AntiVirus Corporate Edition 10.0, or newer products, LiveUpdate definitions are updated daily. These products include newer technology.

    If you use Norton AntiVirus 2005, Symantec AntiVirus Corporate Edition 9.0, or earlier products, LiveUpdate definitions are updated weekly. The exception is major outbreaks, when definitions are updated more often.

  • Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted daily. You should download the definitions from the Symantec Security Response Web site and manually install them.

The latest Intelligent Updater virus definitions can be obtained here: Intelligent Updater virus definitions . For detailed instructions read the document: How to update virus definition files using the Intelligent Updater .

3. To run a full system scan
  1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.

    For Norton AntiVirus consumer products: Read the document: How to configure Norton AntiVirus to scan all files.

    For Symantec AntiVirus Enterprise products: Read the document: How to verify that a Symantec Corporate antivirus product is set to scan all files.

  2. Run a full system scan.
  3. If any files are detected, follow the instructions displayed by your antivirus program.
Important: If you are unable to start your Symantec antivirus product or the product reports that it cannot delete a detected file, you may need to stop the risk from running in order to remove it. To do this, run the scan in Safe mode. For instructions, read the document, How to start the computer in Safe Mode . Once you have restarted in Safe mode, run the scan again.

After the files are deleted, restart the computer in Normal mode and proceed with the next section.

Warning messages may be displayed when the computer is restarted, since the threat may not be fully removed at this point. You can ignore these messages and click OK. These messages will not appear when the computer is restarted after the removal instructions have been fully completed. The messages displayed may be similar to the following:

Title: [FILE PATH]
Message body: Windows cannot find [FILE NAME]. Make sure you typed the name correctly, and then try again. To search for a file, click the Start button, and then click Search.

4. To delete the value from the registry
Important: Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified subkeys only. For instructions refer to the document: How to make a backup of the Windows registry .
  1. Click Start > Run.
  2. Type regedit
  3. Click OK.

    Note: If the registry editor fails to open the threat may have modified the registry to prevent access to the registry editor. Security Response has developed a tool to resolve this problem. Download and run this tool, and then continue with the removal.
  4. Navigate to and delete the following entries:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Drivers32\"midi1" = "[RANDOM CHARACTERS][RANDOM DIGITS].dll"

  5. Navigate to and delete the following subkey:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Browser Helper Objects\{[RANDOM CLSID]}

  6. Exit the Registry Editor.

    Note: If the risk creates or modifies registry subkeys or entries under HKEY_CURRENT_USER, it is possible that it created them for every user on the compromised computer. To ensure that all registry subkeys or entries are removed or restored, log on using each user account and check for any HKEY_CURRENT_USER items listed above.

Writeup By: Liam O Murchu