Protecting Code in an Excel Workbook?

Question

I want to produce an Excel workbook that will contain proprietary formulas and other intellectual property. I will most likely produce this workbook in Visual Studio 2010 wi

Answer 1

If you Save the workbook with a password to open as an XLSB (Note this NOT Protect Workbook Structure etc) the workbook is encrypted with reasonably secure encryption (stronger in Excel 2013).
But the user has to supply a password to open it, which is not suitable for some useage scenarios.

All other forms of Excel protection are relatively weak.

Securing code in Excel is best done using a C++ XLL.
Next best is a VB6 DLL (but this is now a dead technology and won't work in 64-bit Excel)
Next best is obfuscated .NET, but you really need to be using the kind of .NET XLL interface provided by Addin Express or XL DNA to avoid the poor performance characteristics of .NET Interop and VSTO.