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.
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
Description Created: Mikko Hypponen, F-Secure