Q:

Can I password protect an Excel macro? 

I know it is possible to password protect an entire Excel workbook, but can I have the workbook open (no password) and yet password protect just the macro? 
(I'm using Excel 2007.) 
Update: to be clear, I'm looking to password protect access to viewing the macro, not to running it.  So, everyone should be able to run it but only I can access the source code. 

A:

To add to @music2myear's answer, you can also protect the workbook's VBA code, so the user can't read it to get the password.   In the VBE just right-click on the project and choose VBAProject Properties and click the Protection tab.