Why was excel.exe deleted by Norton Power Eraser

Following problems starting a Norton Internet Security scan, I ran Norton Power Eraser.  This cured the scan problem but also deleted excel.exe and msoffice.exe.  The computer is running Windows 8 and the Excel version is Excel 97.  I have been using this machine for 3 months with no problem before this week.  Does anyone know what the problem is with Excel and will it be safe to reinstall it?

 

Thanks,

Graham.