Virus:X97M/Laroux is the first real Microsoft Excel macro virus was found in July 1996.
Laroux was written in Visual Basic for Applications (VBA), a macro language based on Visual Basic. This virus is be able to operate under Excel 5.x and 7.x under Windows 3.x, Windows 95 and Windows NT. It also works under localized version of Excel (for example, versions of Excel translated to French or German). This virus does not work under any version of Excel for Macintosh or Excel 3.x or 4.x for Windows.
ExcelMacro/Laroux is not intentionally destructive and contains no payload; it just replicates.
At the time, Laroux was one of the most common viruses.
Laroux consists of two macros, auto_open and check_files. The auto_open macro executes whenever an infected Spreadsheet is opened, followed by the check_files macro which determines the startup path of Excel.
If there is no file named PERSONAL.XLS in the startup path, the virus creates one. This file contains a module called "laroux".
Once the Excel environment has been infected by this virus, the virus will always be active when Excel is loaded and will infect any new Excel workbooks that are created as well as old workbooks when they are accessed.
If an infected workbook resides on a write-protected floppy, an error will occur when Excel tries to open it and the virus will not be able to replicate.
PERSONAL.XLS is the default filename for any macros recorded under Excel. Thus you might have PERSONAL.XLS on your system even though you are not infected by this virus.
The startup path is by default set as \MSOFFICE\EXCEL\XLSTART, but it can be changed from Excel's Tools/Options/General/Alternate Startup File menu option.
Some of the Laroux variants use PLDT.XLS instead of PERSONAL.XLS and thus are sometimes called XM/PLDT virus.
See also: Concept.