Threat Explorer

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Downloader.Tooncom

Downloader.Tooncom

Discovered:
27 October 2003
Updated:
13 February 2007
Also Known As:
TrojanDownloader.Win32.Tooncom
Systems Affected:
Windows

Downloader.Tooncom is a Trojan Horse that consists of two files, Loader.exe and iedll.exe.

This Trojan overwrites the Windows Hosts file, which is used for name resolution. The Trojan also modifies the Internet Explorer Search and Home pages, as well as Favorites.



The following instructions discuss how to fix the Windows host file so that the added name resolution entries do not forward you to 66.40.16.131.
  1. Using Windows Explorer, look for the Windows host file in the following locations, if the locations exist:
    • C:\Windows\System32\Drivers\Etc\hosts
    • C:\Windows\hosts
    • C:\Winnt\System32\Drivers\Etc\hosts
    • C:\Winnt\hosts
    • D:\Windows\System32\Drivers\Etc\hosts
    • D:\Windows\hosts
    • D:\Winnt\System32\Drivers\Etc\hosts
    • D:\Winnt\hosts

  2. For each \hosts file that you find, double-click the file.
  3. When the "Open With" dialog box appears, scroll through the list and select Notepad. Do not check the "Always open this program with. . ." box.
  4. Within the file, delete any lines that begin with 66.40.16.131.
  5. Save the host file.


Antivirus Protection Dates

  • Initial Rapid Release version 27 October 2003
  • Latest Rapid Release version 01 October 2017 revision 018
  • Initial Daily Certified version 27 October 2003
  • Latest Daily Certified version 02 October 2017 revision 002
  • Initial Weekly Certified release date 29 October 2003
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.


When this Trojan is executed, iedll.exe performs the following actions:
  1. Searches for the Windows host file in the following locations:
    • C:\Windows\System32\Drivers\Etc\Hosts
    • C:\Windows\Hosts
    • C:\Winnt\System32\Drivers\Etc\Hosts
    • C:\Winnt\Hosts
    • D:\Windows\System32\Drivers\Etc\Hosts
    • D:\Windows\Hosts
    • D:\Winnt\System32\Drivers\Etc\Hosts
    • D:\Winnt\Hosts

  2. Deletes all the entries in the files it finds (except those for "localhost") and creates the following entries:

    66.40.16.131 livesexlist.com
    66.40.16.131 lanasbigboobs.com
    66.40.16.131 thumbnailpost.com
    66.40.16.131 adult-series.com
    66.40.16.131 www.livesexlist.com
    66.40.16.131 www.lanasbigboobs.com
    66.40.16.131 www.thumbnailpost.com
    66.40.16.131 www.adult-series.com

    The result of this action is that if you attempt to go to the Web sites added to the Hosts file in step 2, you will be redirected to the IP address, 66.40.16.131. Communication with other hosts may be disrupted, depending on your local DNS configuration.

  3. Attempts to contact the host, tooncomics.com, and then download the file, Loader.exe.

  4. Executes the file, Loader.exe.

When this Trojan is executed, Loader.exe performs the following actions:
  1. Adds these values:

    "loader2"="1"

    "loaderGUID"="CLSID"

    to the registry key:

    HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer

  2. Sets the Internet Explorer Home Page and Search Page to:

    http:/ /thesten.com/main/sp.html

    by modifying the following registry keys:

    HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main\Search Page
    HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main\Search Bar
    HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main\Start Page
    HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\SearchURL
    HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Search\SearchAssistant

  3. Adds the following shortcuts to the Current User's Favorites folder:

    Series Hardcore Pics Sets and Movies.url
    New Porn Pics everyday.url
    Fully categories porn database. Enjoy.url

  4. Attempts to download and then execute iedll.exe from thesten.com.


Recommendations

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.

Disable System Restore (Windows Me/XP).
  1. Update the virus definitions.
  2. Restart the computer in Safe mode or VGA mode.
  3. Run a full system scan and delete all the files detected as Downloader.Tooncom. If necessary, restore the Windows hosts file.
  4. Reset the Internet Explorer home page.
  5. Reset the Internet Explorer Search page.
  6. Remove the links added to Favorites
For specific details on each of these steps, read the following instructions.

1. Disabling 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. Updating 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. Restarting the computer in Safe mode or VGA mode
Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode or VGA mode.
  • For Windows 95, 98, Me, 2000, or XP users, restart the computer in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."
  • For Windows NT 4 users, restart the computer in VGA mode.

4. Scanning for and deleting the infected files
  1. Start your Symantec antivirus program 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 Downloader.Tooncom, click Delete.
  4. If you are having problems connecting to specific Web sites, restore the Windows hosts file from a known clean backup, or edit it and remove the text that the Trojan added. Refer to the "Additional Information" section for instructions.

5. Resetting the Internet Explorer home page
  1. Start Microsoft Internet Explorer.
  2. Connect to the Internet and go to the page that you want to set as your home page.
  3. Click Tools, and then click Internet Options.
  4. In the Home page section of the General tab, click Use Current, and then click OK.


6. Resetting the Internet Explorer Search page
  1. Start Microsoft Internet Explorer.
  2. Click the Search icon on the toolbar.
  3. In the Search pane, click Customize.
  4. Click Reset.
  5. Click Autosearch Settings.
  6. Choose a search site from the drop-down list, and then click OK.
  7. Click OK.

7. Removing links added to Favorites
  1. Start Internet Explorer.
  2. Click Favorites, and then Organize Favorites.
  3. Delete the links to the pornographic Web sites that the Trojan inserted.


Writeup By: Fergal Ladley