Well I understand obtaining the password is pretty easy from 3rd party software, but good to have anyway, belts and braces.
As far as EverythingAccess is concerned, if there is enough copyright information and contact details on each part of the code, hopefully Wayne Philips would see that and ask the originators of the software first before pursuing any decoding. So all in all, placing the serial numbers in a module is at least one of the safest ways to ensure your code is relatively secure and people cannot simply pass on their purchase of a piece of software to anyone one for free use. After all, what would be the point of spending many months developing something.
Unfortunately no system of security can be 100% secure even for a MS Access db even though you can hide the code using an accde file. I'm surprised that Microsoft hasn't introduced such a feature in MS Excel.