XLS Padlock's Formula Protection is a strong security feature for Excel workbooks because original formulas do not exist anymore in the secured workbook: they are replaced by cryptic formulas only recognized by secure applications. Of course, formulas and the workbook still work as expected.
Basics of XLS Padlock are quickly reviewed through this short video presentation.
XLS Padlock has an integrated VBA compiler: it can turn your Excel VBA code into working bytecode not accessible to final users. Turning parts of your VBA macros into compiled code allows you to secure them: the original code does not exist anymore and it cannot be copied.
This video tutorial aims to show you how to protect a simple Excel VBA function: