X97M/Manalo is an Excel macro virus.
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
When an infected workbook is opened, X97M/Manalo.A checks if file "MANALO.XLS" exists in the Excel's startup directory. If the file does not exist, the virus creates a new workbook, infects it and saves it to there.
At October 3rd, 1999 and every day after that the virus activates its payload. At this time it shows a hidden sheet with some text and a flag.
X97M/Manalo.D is a modified variant of X97M/Manalo.A. It creates a workbook, "C B I.XLS", to Excel's statup directory.
This variant activates its payload at September 27th, 1999 and every day after that when it attempts to show an hidden sheet.
Technical Details: Sami Rautiainen, F-Secure