X97M/Diablo is an Excel 97 macro virus.
Depending on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the suspect file, or ask you for a desired action.
More information on the scanning and removal options available in your F-Secure product can be found in the Help Center.
You may also refer to the Knowledge Base on the F-Secure Community site for more information.
When a sheet is activated from an infected workbook, X97M/Diablo.A if a workbook "PERSONAL.XLS" is exists in the Excel's startup directory. If the workbook does not exist, the virus creates a new workbook and infects it. After that it infects all workbooks that are opened.
The virus activates its payload in the random dates, when it changes the size of toolbar buttons to large.