W97M.Tang

SUMMARY

W97M.Tang is the macro module of W32.HLLW.Tang@mm. It infects Microsoft Word documents and templates.

Protection

• Virus Definitions (LiveUpdate™ Weekly) February 19, 2003
• Virus Definitions (Intelligent Updater) February 18, 2003

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: Low

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When W97M.Tang is executed, it does the following:

1. Turns off the following Microsoft Word options:
   • Microsoft Macro Virus Protection
   • Save Normal Prompt
   • Confirm Conversions
     
2. Adds the values:
   
   AccessVBOM      1
   Level                      1
   
   to the registry keys:
   
   HKEY_CURRENT_USERSoftwareMicrosoftOffice<office version>WordSecurity
   HKEY_CURRENT_USERSoftwareMicrosoftOffice<office version>ExcelSecurity
   
   NOTE: <office version> varies with the version of Microsoft Office you have installed.
   
3. Disables the following menu items:
   • Tools>Macro
   • Tools>Customize...
   • Macro>Security...
   • Macro>Macros...
   • View>Toolsbars
     
4. Infects the Normal.dot template and the active document.
   
5. Adds the value:
   
   Installed                 1
   
   to the registry key:
   
   HKEY_CURRENT_USERSoftwareed/[rRlf]W32/TaNGMacro
   
6. Overwrites the file, Personal.xls, in the Microsoft Excel Startup folder.
   
   NOTE: The infected Excel worksheets will be detected as X97M.Tang.
   
7. Does one of the following:
   • If the file %System%MSTnglnk.exe exists, it executes this file.
   • If the file %System%MSTnglnk.exe does not exist, it inserts W32.HLLW.Tang@mm as %System%MSTnglnk.exe.
     
     NOTE: %System% is a variable. The virus locates the System folder and copies W32.HLLW.Tang@mm to that location. By default, this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).

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.Tang.
3. Reverse the changes that the worm made 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 the 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), in the "Protection" section, at the top of this writeup.
• 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), in the "Protection" section, at the top of this writeup.
  
  The Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.

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.Tang, click Repair.

3. Reversing the registry changes

CAUTION: Symantec strongly recommends that you back up the registry before you make 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.

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_CURRENT_USERSoftwareMicrosoftOffice<office.version>WordSecurity
   
4. In the right pane, delete these values:
   
   AccessVBOM
   Level
   
5. Navigate to the key:
   
   HKEY_CURRENT_USERSoftwareMicrosoftOffice<office.version>ExcelSecurity
   
6. In the right pane, delete the values:
   
   AccessVBOM
   Level
   
7. Delete the registry key:
   
   HKEY_CURRENT_USERSoftwareed/[rRlf]W32/TaNG
   
8. Exit the Registry Editor.