W97M.Trug.B

SUMMARY

W97M.Trug.B is a macro virus that infects Microsoft Word documents when they are opened or closed.

W97M.Trug.B attempts to hide its malicious actions and may delete several files from the system.

Protection

• Virus Definitions (LiveUpdate™ Weekly) March 10, 2004
• Virus Definitions (Intelligent Updater) March 10, 2004

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
• Payload Trigger: 2nd, 18th, and 27th of each month.
• Payload: On the 27th of each month, autoexec.bat will be created on the root of the C: drive. On the 2nd and 18th, TRUG.vbs will be created on C:WindowsSystem.
• Deletes Files: Several system files will be deleted if the system is running Windows 9x and the second payload has been executed.
• Causes System Instability: This virus contains several bugs that may cause Microsoft Word to crash.
• Compromises Security Settings: Lowers the macro virus protection settings for Microsoft Word.

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

The W97M.Trug.B macro module is executed when Microsoft Word documents are opened or closed.

When the viral macro module runs, it does the following:

1. Disables several Microsoft Word toolbars.
   
   
2. Hooks the shortcut keys so that the macro modules cannot be seen.
   
   
3. Disables macro virus protection.
   
   Note: The first three actions are an attempt by the virus to hide itself from you.
   
   
4. Deletes all the macro modules from the Microsoft Word global template file, Normal.dot, except for the ThisDocument module.
   
   
5. Deletes all the macro modules from all the opened documents, except for the ThisDocument module.
   
   
6. Checks whether the Normal.dot file is infected. If the file is not, it adds itself to the Normal.dot file by importing its viral code from the exported Trugfile.txt. file. The module it adds is named ThisDocument. Once the Normal.dot file is infected, the virus attempts to infect the active document in the same way.
   
   
7. Calls the first payload routine. This payload is to create the file, C:Autoexec.bat, on the 27th of each month. The Autoexec.bat file attempts to format the C and D drives. The infected Autoexec.bat file is detected as BAT.Trojan.
   
   
8. Calls the second payload routine. The second payload is executed on the 2nd and the 18th of each month. This payload creates the file, C:WindowsSystemTRUG.vbs. TRUG.vbs is detected as W97M.Trug.B.
   
   
9. Adds the value:
   
   "SystemSettingf" = "C:WindowsTRUG.vbs"
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   so that the virus runs when you start Windows
   
   Note: If the operating system is Windows 95/98/Me and this payload is executed, and if you restart the computer, the system files will be deleted and the computer will no longer start.
   

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

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

1. Update the virus definitions.
2. Run a full system scan and repair all the files detected as W97M.Trug.B.
3. Delete the value that was added to the registry.

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

1. 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.

2. Scanning for and repairing 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 W97M.Trug.B, click Repair.
   

3. Deleting the value from 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
   
   Then click OK. (The Registry Editor opens.)
   
   
3. Navigate to the key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
4. In the right pane, delete the value:
   
   "SystemSettingf" = "C:WindowsTRUG.vbs"
   
   
5. Exit the Registry Editor.