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Discovered: June 24, 2004
Updated: February 13, 2007 12:24:36 PM
Type: Trojan Horse
Systems Affected: Windows

JS.Scob.Trojan is a simple Trojan that executes a JavaScript file from a remote server.

The Trojan's dropper sets it as the document footer for all pages served by IIS Web sites on the infected computer.

Antivirus Protection Dates

  • Initial Rapid Release version June 25, 2004
  • Latest Rapid Release version August 20, 2008 revision 017
  • Initial Daily Certified version June 25, 2004
  • Latest Daily Certified version August 20, 2008 revision 016
  • Initial Weekly Certified release date June 25, 2004

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

Technical Description

The JS.Scob.Trojan dropper is detected as Trojan.Scob!dr. When it is executed, the dropper performs the following actions on the IIS Web server:

  1. Drops ads.vbs into the current folder.

    Note: This file is a legitimate file and is not detected.

  2. Drops three files, named %System%\inetsrv\iisXXX.dll, where XXX are three hexidecimal digits.

    • %System% is a variable. The trojan locates the System folder and copies itself to that location. By default, this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).
    • These files contain Javascript and are detected as JS.Scob.Trojan.

  3. Modifies the configuration of IIS Web sites on the infected computer to make one of the iisXXX.dll files the document footer.

    An infected computer will have Document Footer settings like this:

    This causes IIS to append JS.Scob.Trojan to pages served by the Web server, such as .html, .jpeg, and .gif files.

    Note: These files are detected as JS.Scob.Trojan!inf.

The Javascript, JS.Scob.Trojan and JS.Scob.Trojan!inf do the following on the client side:
  1. If the file is not accessed through HTTPS and the Trojan has not set a currently valid cookie on the computer, it launches a JavaScript file located at

    Note: At the time of this writing, the remote file is not available.

  2. The Trojan then sets a cookie which expires in one week. The cookie begins with the characters "trk716".

    Once the Trojan is triggered, it will not be triggered again until a week later.


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, repair all the files detected as JS.Scob.Trojan!inf, and delete all files detected as JS.Scob.Trojan, JS.Scob.Trojan!inf or JS.Scob.Trojan!dr.
  4. Reset the document footer setting of IIS web sites.
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, re-enable 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: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
  • Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).

    The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

3. To scan for and repair the infected files
  1. Start your Symantec antivirus software and make sure that it is configured to scan all the files.
  2. Run a full system scan.
  3. If any files are detected as infected with JS.Scob.Trojan!inf, click Repair.
  4. If any files are detected as JS.Scob.Trojan or JS.Scob.Trojan!inf, click Delete.

4. To reset the document footer setting of IIS web sites.

Note: This step only applies if IIS is installed on the infected computer.
  1. In the Internet Services Manager, right click on each Web site and go to Properties.
  2. To restore the settings to their original values, delete the dll path in the text box and uncheck the "Enable Document Footer" check box. If you use a custom document footer in IIS, browse to the file's location and select it as your document footer.

Writeup By: Paul Mangan