Sale of spreadsheet advice

Hi,

I've created a spreadsheet that I want to offer for sale.

I've protected all cells with formula and those not needed to use the program. The only cells that can be selected/changed are those that need the values for the calculations.

How do I protect the sheet from being saved/stolen when trialed by possible customers? Is this possible?

Any other advice on the issue would be appreciated.

Thank.

It's fairly common knowledge that Excel files do not have "bullet proof" security. The general intent of Excel passwords is to prevent accidental meddling and provide somewhat of an obstacle to intentional meddling. Think of it like locking the door to your home. Is it impregnable when a dishonest person could just break a window and climb in? The intent is to signal to honest people that you don't want them entering certain areas. Any person with fairly unimpressive technical skills could find a way to circumvent your security with only moderate effort.

For real security, development should be in compiled code, as generated by C++, VB, etc.

There's pretty much no way you're going to protect a worksheet that can't be broken. Excel isn't a secure application. Workbook/worksheet protection, and passwords to open the file itself, will only keep novice Excel users from saving (or "stealing") your spreadsheet and formulas.

But, in an effort to thwart the novices, be sure to protect your worksheets, workbook, VBA modules and if necessary add a password to even open the workbook. Of all of those protections, the password to open the book is probably the strongest, but once it's open there's little you can do to stop someone who wants to get into the things you want to keep hidden.

I believe there are third party applications that can modify excel files, or convert them to a different type of file, but I can't vouch for any of them (as I have not used them, personally).

A "trial period" (aka 'time bomb') could be implemented, but it would still require Excel macros to create and verify dates, and therefore would be easy to circumvent for anyone with Excel and Google since they could get into the code to see what it does before the trial period is up.

As mentioned, there aren't really any secure parts to Excel. You could compile all of your code into a DLL file, and simply pass data back and forth between Excel and your functions and not rely on any in-sheet formulas or code, but even DLL's can be decompiled (although it would keep the vast majority of users out of your functions).