O97M.Tristate

O97M.Tristate infects Microsoft Word 97 documents, Microsoft Excel 97 spreadsheets, and Microsoft PowerPoint slides. The infection routine in each Microsoft Office application is triggered differently, as described in detail in the following paragraphs.

From an infected Word 97 document
The virus does not add a new Visual Basic Application (VBA) module but inserts its viral code into the default VBA module called ThisDocument. The following viral routine is activated when an infected Word document is closed:

• Crossing to Excel:
  If there is no file called BOOK1 in the Excel startup directory (usually called XLSTART), the virus turns off Excel macro virus protection (found under Tools Options General). Then it creates a viral workbook called BOOK1 in the Excel startup directory.
  
• Crossing to PowerPoint:
  If there is no Triplicate module in the Blank Presentation.POT PowerPoint template (usually in the TEMPLATES directory), the virus turns off PowerPoint macro virus protection (found under Tools Options General). Then it adds a viral module called Triplicate to Blank Presentation.POT and a basic AutoShape object that covers the entire slide. The viral module is linked to the AutoShape object.
  
• Re-infecting the Word document being closed, if necessary:
  If the ThisDocument module of the document being closed does not match what the virus expects, the virus replaces the content of the ThisDocument module with its viral code.

From an infected Excel 97 spreadsheet:
The virus does not add a new Visual Basic Application (VBA) module but inserts its viral code into the default VBA module called ThisWorkbook. The following viral routine is activated when the infected workbook is deactivated (as in editing another workbook or opening a new one):

• Crossing to Word:
  If there is no file called BOOK1 in the Excel startup directory (usually called XLSTART), the virus turns off Excel and PowerPoint macro virus protection (found under Tools Options General). Then the virus replaces the content of the ThisDocument module of the Word Normal Template (usually called NORMAL.DOT) with its viral code.
  
• Crossing to PowerPoint:
  If there is no file called BOOK1 in the Excel startup directory (usually called XLSTART), and there is no Triplicate module in the Blank Presentation.POT PowerPoint template (usually in the TEMPLATES directory), the virus adds a viral module called Triplicate to Blank Presentation.POT and a basic AutoShape object that covers the entire slide. The viral module is linked to the AutoShape object.
  
• Re-infecting the Excel spreadsheet being closed, if necessary:
  If the ThisWorkbook module of the active spreadsheet does not match what the virus expects, the virus inserts its viral code into the ThisWorkbook module.

From an infected PowerPoint 97 presentation:
In a PowerPoint slide, the virus adds a new Visual Basic Application (VBA) module called Triplicate. The user then has a one in seven chance that the following viral routine will be activated when an infected slide is clicked in a slide show view:

• Crossing to Word:
  If there is no file called BOOK1 in the Excel startup directory (usually called XLSTART), the virus turns off Excel and PowerPoint macro virus protection (found under Tools > Options > General). Then the virus replaces the content of the ThisDocument module of the Word Normal Template (usually called NORMAL.DOT) with its viral code.
  
• Crossing to Excel:
  If there is no file called BOOK1 in the Excel startup directory (usually called XLSTART), the virus turns off Excel macro virus protection (found under Tools > Options > General). Then it creates a viral workbook called BOOK1 in the Excel startup directory.
  
• Re-infecting the PowerPoint template, if necessary:
  If there is no file called BOOK1 in the Excel startup directory (usually called XLSTART), and there is no Triplicate module in the Blank Presentation.POT PowerPoint template (usually in the TEMPLATES directory), the virus adds a viral module called Triplicate to Blank Presentation.POT and a basic AutoShape object that covers the entire slide. The viral module is linked to the AutoShape object.

In PowerPoint, the virus does not directly infect a PowerPoint slide. It infects the Blank Presentation.POT template. Once the template is infected, every new PowerPoint slide that is based on this Blank Presentation template contains the viral module and AutoShape.

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.

Summary