X97M/Friend is a Excel 97 class infector.
Allow F-Secure Anti-Virus to disinfect the relevant files.
For more general information on disinfection, please see Removal Instructions.
When an infected workbook is opened, X97M/Friend.A disables Excel's built-in macro virus protection. Then it creates a workbook into Excel's startup directory, "sys.xls", and infects it. During infection the virus creates a temporary file, "C:\office.sys".
After that has been done and the Excel has been restarted, every workbook that is closed will be infected.
X97M/Friend.B is a slightly modified variant from X97M/Friend.A.
Technical Details: Sami Rautiainen, F-Secure