Trojan.Admincash.B

SUMMARY

Trojan.Admincash.B is a Trojan horse that infects the Explorer.exe file and downloads adware and dialers.

Protection

• Virus Definitions (LiveUpdate™ Weekly) April 27, 2005
• Virus Definitions (Intelligent Updater) April 26, 2005

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Medium
• Modifies Files: Infects the explorer.exe file.
• Compromises Security Settings: Attempts to disable several Windows security features.

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When Trojan.Admincash.B is executed, it performs the following actions:

1. Creates copies of itself as:
   
   
   • %Windir%explorer.new
   • %System%dllcacheexplorer.exe
   • %System%svhost.exe
   • %System%[Trojan file name]
     
     Notes:
   • %System% is a variable that refers to the System folder. By default this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
   • %Windir% is a variable that refers to the Windows installation folder. By default, this is C:Windows (Windows 95/98/Me/XP) or C:Winnt (Windows NT/2000).
     
     
2. Creates the mutex "bayan", so that only one instance of the Trojan runs at the one time.
   
   
3. Adds the value:
   
   "System backup" = "%System%[Trojan file name]"
   
   to the registry subkeys:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRun
   
   so that the Trojan runs every time Windows starts.
   
   
4. Adds the following line in the [Windows] section of the Win.ini file, on computers running Windows 95/98/ME:
   
   run=%System%svhost.exe
   
   
5. Adds the following line to the Wininit.ini file:
   
   [Rename]
   %Windir%explorer.exe=%Windir%explorer.new
   
   
6. Adds the value:
   
   "run" = "%System%svhost.exe"
   
   to the registry subkey:
   
   HKEY_CURRENT_USERSoftwareMicrosoftWindows NTCurrentVersionWindows
   
   Note: The Trojan adds the value to the above registry subkey on computers running Windows NT/2000/XP only.
   
   
7. Adds the value:
   
   "DisableSR" = "1"
   
   to the registry subkeys:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows NTCurrentVersionSystemRestore
   HKEY_CURRENT_USERSoftwareMicrosoftWindows NTCurrentVersionSystemRestore
   
   to disable system restore.
   
   
8. Adds the values:
   
   "NoAutoUpdate" = "1"
   "AUOptions" = "1"
   
   to the registry subkeys:
   
   HKEY_LOCAL_MACHINESOFTWAREPoliciesMicrosoftWindowsWindowsUpdateAU
   HKEY_CURRENT_USERSoftwarePoliciesMicrosoftWindowsWindowsUpdateAU
   
   to disable automatic Windows Updates.
   
   
9. Adds the values:
   
   "FirewallDisableNotify" = "1"
   "UpdatesDisableNotify" = "1"
   "AntiVirusDisableNotify" = "1"
   
   to the registry subkeys:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftSecurity Center
   HKEY_CURRENT_USERSoftwareMicrosoftSecurity Center
   
   to disable notification of firewall, antivirus, and update status through the Windows Security Center.
   
   
10. Adds the value:
    
    "SelfLimit" = "1"
    
    to the registry subkeys:
    
    HKEY_LOCAL_MACHINESOFTWAREMicrosoftInternet ExplorerMain
    HKEY_CURRENT_USERSOFTWAREMicrosoftInternet ExplorerMain
    
    as an infection marker.
    
    
11. Infects the file %Windir%explorer.exe.
    
    
12. Downloads several adware and dialer programs from the advadmin.biz domain.

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. Restore Explorer.exe
2. Disable System Restore (Windows Me/XP).
3. Update the virus definitions.
4. Run a full system scan and delete all the files detected as Trojan.Admincash.B.
5. Delete any values added to the registry.
6. Restore the Windows Security Center
7. Edit the Win.ini and Wininit.ini files
   

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

1. To restore Explorer.exe
Important: This must be done before you restart your computer, otherwise Windows may not restart properly.

1. Click Start > Programs > Accessories > Command Prompt
2. Type sfc /scannow
3. Insert the Windows installation CD when prompted.
   

2. 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

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).

3. 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 document: Virus Definitions (LiveUpdate).
• 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. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the document: Virus Definitions (Intelligent Updater).
  
  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.

4. 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.Admincash.B, click Delete.
   
   Note: If your Symantec antivirus product reports that it cannot delete an infected file, Windows may be using the file. To fix 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 section 4.
   
   Warning messages may be displayed when the computer is restarted, as the threat has not been fully removed at this point. Please ignore these messages and just 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.
   

5. 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.
   
   
4. Navigate to the subkeys:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRun
   
   
5. In the right pane, delete the value:
   
   "System backup" = "%System%[Trojan file name]"
   
   
6. Navigate to the subkey:
   
   HKEY_CURRENT_USERSoftwareMicrosoftWindows NTCurrentVersionWindows
   
   
7. In the right pane, delete the value:
   
   "run" = "%System%svhost.exe"
   
   
8. Navigate to the subkeys:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftInternet ExplorerMain
   HKEY_CURRENT_USERSOFTWAREMicrosoftInternet ExplorerMain
   
   
9. In the right pane, delete the value:
   
   "SelfLimit" = "1"
   
   
10. Exit the Registry Editor.
    
    

6. To restore the Windows Security Center
This threat attempts to disable the features in the Windows Security Center, available in Windows XP Service Pack 2. If you are running Windows XP Service Pack 2 and would like to restore the full functionality of the Windows Security Center, please complete the following steps:

Important: If your computer is connected to a domain, you may not be able to adjust these settings. If so, contact your network administrator for more information.

1. Click Start > Control Panel.
2. Double-click the Security Center.
3. In the right pane, click Windows Firewall. The Windows Firewall appears.
4. Select On.
5. Click OK to close the Windows Firewall.
6. In the left pane of the Security Center, select Change the way Security Center alerts me.
7. Click Alert Settings.
8. Select Alert Settings, Firewall, and Virus Protection.
9. Click OK
10. Click Automatic Updates.
11. Select Automatic.
12. Click OK.
13. Exit the Security Center
    
    

7. Edit the Win.ini and Wininit.ini files
If you are running Windows 95/98/Me, follow these steps:

1. Click Start > Run.
2. Type the following:
   
   edit %Windir%win.ini
   
   and then click OK.
   
   Note: %Windir% is a variable that refers to the Windows installation folder. By default, this is C:Windows or C:Winnt.
   
   
3. In the [windows] section of the file, look for a line similar to:
   
   run=%System%svhost.exe
   
   Note: %System% is a variable that refers to the System folder. By default this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
   
   
4. If this line exists, delete everything to the right of run=
5. Click File > Save.
6. Click File > Exit.
7. Click Start > Run.
8. Type the following:
   
   edit c:windowswininit.ini
   
   and then click OK.
   
   Note: If Windows is installed in a different location, make the appropriate path substitution.
   
   
9. In the [windows] section of the file, look for a line similar to:
   
   [Rename]
   %Windir%explorer.exe=%Windir%explorer.new
   
   Note: %Windir% is a variable that refers to the Windows installation folder. By default, this is C:Windows or C:Winnt.
   
   
10. If this line exists, delete it.
11. Click File > Save.
12. Click File > Exit.