XM.Laroux

SUMMARY

XM.Laroux is a virus first discovered in July 1996 in Africa and Alaska and is the first working Excel macro virus found in general circulation. The actual virus code consists of two macros called Auto_Open and Check_Files. The macros are stored in a hidden datasheet named "laroux".

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
• Target of Infection: Microsoft Excel spreadsheets

TECHNICAL DETAILS

In infected spreadsheet files (Excel workbooks), the "laroux" datasheet is not readily visible (it is hidden). When an infected spreadsheet is first opened on a system, the Auto_Open macro is automatically run by Excel, which in turn runs the Check_Files macro. This happens each time a worksheet is activated.

The Check_Files macro then copies the worksheet with the virus code into a spreadsheet file stored in the Excel startup directory named Personal.xls. (By default, this directory is MSOfficeExcelXLStart.) Personal.xls is the "global macro spreadsheet;" macros stored there are automatically available to all other Excel spreadsheets on the system. Copying these macros to Personal.xls enables the infection of all other spreadsheets opened or created on the infected system in the future.

XM.Laroux contains no deliberately destructive payloads: it exists only to replicate. XM.Laroux only works on Microsoft Windows operating systems using Excel versions 5 and 7. It does not work in the Macintosh environment.

XM.Laroux is written in English.

XM.Laroux was discovered in a limited distribution and has showed no sign of rapid spread.

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.