X97M.Laroux.TY

SUMMARY

This virus infects Microsoft Excel 97 spreadsheets. The virus does not contain a malicious payload. It disables the Microsoft Excel macro virus protection option and removes the Microsoft Excel macro toolbar from the Tools menu.

Protection

• Virus Definitions (Intelligent Updater) July 21, 2000

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

This Microsoft Excel 97 macro virus adds a Visual Basic Application (VBA) module into open spreadsheets.

The infection routine is triggered when a file is opened. Upon execution, the virus attempts to modify the registry key:

HKLMSoftwareMicrosoftOffice8.0ExcelMicrosoft ExcelOptions6

The virus disables the Microsoft Excel macro virus protection option. It also removes the macro toolbar from the Tools menu.

This macro virus creates a Personal.xls file in the Excel Startup folder (usually officeXLStart). This loads the viral code every time Excel is opened.

The virus is polymorphic and changes the module name upon infecting the Personal.xls. The module always has a two-character name. The module name does not change when infecting documents, only when infecting Personal.xls.

When infecting, the virus checks whether the spreadsheet is already infected. This prevents the virus from infecting a file twice

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

To enable macro virus protection in Excel:

1. Click Tools Options General.
2. Click Macro virus protection.

To restore the Excel macro Tool menu:

1. Click Tools Customize Commands.
2. Click Tools.
3. Drag the Macros... option from the right-hand side to the appropriate menu.