In the Visual Basic Editor you can protect each module with a password. By doing so only users that know the password can open the module.
This is a limited form of protection as Excel passwords are not the most secure but it would stop any casual prying.
Martin Liss
To protect the code, open the Excel Workbook and go to Tools>Macro>Visual Basic Editor (Alt+F11). Now, from within the VBE go to Tools>VBAProject Properties and then click the Protection page tab and then check "Lock project from viewing" and then enter your password and again to confirm it.
This is a limited form of protection as Excel passwords are not the most secure but it would stop any casual prying.