Beginning with Excel 2007, there are still four security levels but their meanings are subtly different from those in Excel 2003 and earlier.
To change the macro security level
To enable macros in the Option B workbooks
When an Option B workbook is opened, a macro runs that reads some identity information from the registration form and hides the red “Macros are disabled” warning in the header area of the spreadsheet. In Excel 2010 only (not in earlier versions of Excel), this macro runs only if Excel is already running when you open the workbook.
Therefore for Excel 2010, we strongly recommend that you start Excel 2010 before opening an Option B workbook.