This is a Microsoft Excel macro virus. Sofa spreads to Excel spreadsheets once it has copied its virus code to the default startup directory. It does this by creating a file called \MSOFFICE\EXCEL\STARTUP\BOOK.XLT
Sofa contains these macros: Auto_Open, Auto_Range, Current_Open, and Auto_Close.
Sofa activates by checking the title bar text of Excel to read
Otherwise, the virus just spreads.
Sofa was found in the wild in USA in December 1996.
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.