Trojan.Norio

SUMMARY

Trojan.Norio is a Trojan horse that modifies browser and network settings to direct you to pornographic Web sites. This Trojan horse changes the default Explorer home page and search pages by modifying the registry.

The worm includes a component that can download and execute arbitrary code on your computer.

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Note: At the time of this writing, this Trojan uses the file names, Winupdate.exe and Lookupsys.exe, in the Windows folder.

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Protection

• Virus Definitions (LiveUpdate™ Weekly) September 4, 2003
• Virus Definitions (Intelligent Updater) September 4, 2003

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 50 - 999
• Number of Sites: 3 - 9
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Difficult

Damage

• Damage Level: Medium
• Payload: Downloads and executes arbitrary code; displays popup ads.
• Modifies Files: Adds entries to %Windir%hosts or %WindirSystem32driversetchosts.

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When Trojan.Norio is executed, it does the following:

1. Adds at least one of the following values:
   
   "Windows Update"="<file name>"
   "service"="<file name> delete"
   "service_ls"="<file name> delete"
   "Network Service"="<file name> -sr -0"
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
   
2. Creates the registry key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWinUpdate
   
   which is used to store a unique identification number.
   
   
3. Adds entries to one of the files, %Windir%Hosts or %Windir%System32driversetcHosts.
   These entries may redirect the following URLs to point to the local computer, which may result in error messages when you try to access them:
   
   www.coolwebsearch.org
   coolwebsearch.org
   www.coolwebsearch.info
   coolwebsearch.info
   www.searchcomplete.com
   searchcomplete.com
   www.coolsearcher.net
   coolsearcher.net
   www.adulthyperlinks.com
   adulthyperlinks.com
   www.allhyperlinks.com
   allhyperlinks.com
   www.white-pages.ws
   white-pages.ws
   www.clearsearch.net
   clearsearch.net
   www.youfindall.net
   youfindall.net
   www.coolwwwsearch.com
   coolwwwsearch.com
   www.unipages.cc
   unipages.cc
   www.sexy18.cc
   sexy18.cc
   www.trafficswitcher.com
   trafficswitcher.com
   www.trafficback.com
   trafficback.com
   www.selfbookmark.com
   selfbookmark.com
   
   
4. Modifies the value for:
   
   "SearchURL"
   
   in the registry key:
   
   HKEY_CURRENT_USERSoftwareMicrosoftInternet Explorer
   
   
5. Modifies the values for:
   
   "Search Page"
   "Search Bar"
   
   in the registry key:
   
   HKEY_CURRENT_USERSoftwareMicrosoftInternet ExplorerMain
   
   
6. Modifies the values for:
   
   "Default_Search_URL"
   "Search Page"
   
   in the registry key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftInternet ExplorerMain
   
   
7. Modifies the values for:
   
   "SearchAssistant"
   
   in the registry key:
   
   HKEY_CURRENT_USERSoftwareMicrosoftInternet ExplorerSearch
   
   
8. Modifies the values for:
   
   "SearchAssistant"
   "CustomizeSearch"
   
   in the registry key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftInternet ExplorerSearch
   
   
9. Monitors open Web browser windows. If the title of an open Web page contains strings that the Trojan determines are characteristic of a porn site, it will open another porn site in a new browser window.
   
   
10. Periodically contacts a Web server for instructions. The response contains the URL for a file, which the Trojan will download and execute. This functionality may be used to update the Trojan or run any other code on a compromised system.
    
    
11. The Trojan may delete itself when the computer restarts.

Recommendations

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

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended 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 (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. 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.

REMOVAL

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 and delete all the files detected as Trojan.Norio.
4. Reverse the changes to the registry.
5. Remove the entries that were added to the Hosts file.
6. Reset the Internet Explorer home page.
7. Reset the Internet Explorer search pages.
   

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:

• "How to disable or enable Windows Me System Restore"
• "How to turn off or turn on Windows XP System Restore"

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 delete the infected files

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 as infected with Trojan.Norio, write down the file names, and click Delete.

4. To reverse the changes to the registry

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WARNING: 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 keys only. Read the document, "How to make a backup of the Windows registry," for instructions.

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1. Click Start, and then click Run. (The Run dialog box appears.)
2. Type regedit
   
   and then click OK. (The Registry Editor opens.)
   
   
3. Navigate to the key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
   
4. In the right pane, delete any of these values, or any values that refer to the file names, which were detected as Trojan.Norio:
   
   "Windows Update"="<file name>"
   "service"="<file name> delete"
   "service_ls"="<file name> delete"
   "Network Service"="<file name> -sr -0"
   
   
5. Navigate to and delete the key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWinUpdate
   
   
6. Exit the Registry Editor.

5. To remove the entries from the Hosts file

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Note: The location of the Hosts file may vary, and some computers may not have this file.

For example, if the file exists in Windows 98, it will usually be in C:Windows; and it is located in the C:WINNTsystem32driversetc folder in Windows 2000. There may also be multiple copies of this file in different locations.

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Follow the instructions for your operating system:

• Windows 95/98/Me/NT/2000
  1. Click Start, point to Find or Search, and then click Files or Folders.
  2. Make sure that "Look in" is set to (C:) and that "Include subfolders" is checked.
  3. In the "Named" or "Search for..." box, type:
     
     hosts
     
     
  4. Click Find Now or Search Now.
  5. For each one that you find, note its location. (This is displayed in the "In Folder" column.)
  6. Right-click each Hosts file, and then click "Open With."
  7. Deselect the "Always use this program to open this program" check box.
  8. Scroll through the list of programs and double-click Notepad.
  9. When the file opens,delete all the entries in the Hosts file, except for the following line:
     
     127.0.0.1     localhost
     
     
  10. Close Notepad and save your changes when prompted.
      
      
• Windows XP
  1. Click Start, and then click Search.
  2. Click All files and folders.
  3. In the "All or part of the file name" box, type:
     
     hosts
     
     
  4. Verify that "Look in" is set to "Local Hard Drives" or to (C:).
  5. Click "More advanced options."
  6. Check "Search system folders."
  7. Check "Search subfolders."
  8. Click Search.
  9. Click Find Now or Search Now.
  10. For each one that you find, note its location. (This is displayed in the "In Folder" column.)
  11. Right-click each Hosts file, and then click "Open With."
  12. Deselect the "Always use this program to open this program" check box.
  13. Scroll through the list of programs and double-click Notepad.
  14. delete all the entries in the Hosts file, except for the following line:
      
      127.0.0.1     localhost
      
      
  15. Close Notepad and save your changes when prompted.
      

6. To reset the Internet Explorer home page

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

For additional information, or if this procedure does not work, read the Microsoft® Knowledge Base article, "Home Page Setting Changes Unexpectedly, or You Cannot Change Your Home Page Setting, Article ID 320159."

7. To reset the Internet Explorer Search pages
Follow the instructions for your version of Windows.

Windows 98/Me/2000

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

Windows XP
Because Windows XP is set by default to use animated characters in the search, how you perform this procedure can vary. Read all the instructions before you start.

1. Start Microsoft Internet Explorer.
2. Click the Search button on the toolbar.
3. Do one of the following:
   • If the pane that opens looks similar to this picture:
     
     
     
     
     
     click the word Customize. Then skip to step h.
     
     
   • If the pane that opens has the words "Search Companion" at the top, and the center looks similar to this picture:
     
     
     
     
     
     
     click the "Change preferences" link as shown above. Then proceed with step d.
     
     
4. Click the "Change Internet search behavior" link.
5. Under "Internet Search Behavior," click "With Classic Internet Search."
6. Click OK. Then close Internet Explorer. (Close the program for the change to take effect.)
7. Start Internet Explorer. When the search pane opens, it should now look similar to this:
   
   
   
   
   
   Click the word Customize, and then go on to the next step.
   
   
8. In the Search pane, click Customize.
9. Click Reset.
10. Click Autosearch Settings.
11. Select a search site from the drop-down list, and then click OK.
12. Click OK.
13. Do one of the following:
    • If you were using (or want to continue using) the "Classic Internet Search" panel, stop here (or proceed with the next section).
    • If you want to go back to the "Search Companion" search (it usually has an animated character at the button), proceed with step n.
      
      
14. Click the word Customize again.
15. In the "Customize Search Settings" window, click "Use Search Companion," and then click OK.
16. Close Internet Explorer. The next time that you open it, it will use the Search Companion again.