The macro security levels in Excel changed starting with Excel 2007.
Excel 2000 - 2003
Only macros installed in trusted locations will be allowed to run. All other signed and unsigned macros are disabled. Not available in Excel 2000. Not recommended for use with Option B. (Option B features will only be available with significant setup effort.)
Default setting; only signed macros from trusted sources will be allowed to run. Unsigned macros are automatically disabled. Recommended for Option B, unless you need a lower setting for other reasons.
You can choose whether or not to enable macros in a particular workbook; digital signatures are not required. Acceptable for Option B.
Enable all macros. Not recommended, potentially dangerous code can run.
Excel 2007 - 2013
Disable all macros without notification
Not recommended (Some Option B features will not be available.)
Disable all macros with notification
Acceptable (default setting for Option B)
Disable all macros except digitally signed macros
Recommended for Option B.
Enable all macros
Not recommended (potentially dangerous code can run)