Exactly what are your concerns?
Yes, the password protection on both Workbooks and Worksheets is 'weak' -
there are any number of tools available that will provide a password to
unlock either of those. Password protection for the VBA project is stronger
and less likely to be cracked. I'm not aware of a tool specifically
targeting the VBA project, but one probably exists somewhere.
If you want to prevent prying eyes from viewing your source code, then the
best way is to probably use VB to create a .dll to be distributed with your
..xla and be called from it. That gets you into other areas such as
referencing the library (.dll) file from your .xla application and
registering it in the Windows Registry, etc. The .dll is more secure because
it is the compiled code, not the source, that is distributed.
If your concern is that someone may get into your code and alter it in some
fashion, then consider not only password protecting the VB Project, but also
digitally signing the code. Safest is with one of the rather expensive
digital signatures available from companies like VeriSign, although you can
create one of your own using the Digital Signature tool available as part of
the MS Office Tools. But those signatures can be forged, so are not
absolutes.
