Greetings

I'm currently trying to develop a 'solution' to deliver to my clients. I'm
almost definitely going to be using Excel barring any showstoppers - since
this is what my clients know best. I'm trying to avoid using VSTO, and would
like to be able to stick with Macros and VB code within Excel.

My biggest concern is security. I absolutely need to be able to securely
hide my formulas. The ease of use and familiarity of Excel is only worth
0.1% of the cost of the formulas. My clients don't need to know the formulas,
or how they work, they only need to be able to use them.

I've heard that Excel 2007 password protection is quite abit better than
previous versions - is this true? I realise that nothing is ever 100% secure,
but I need to be sure that the average computer user can't just google a
password breaker and get to the formulas.

What if my clients are running Excel 2003? Would a workbook built in 2007
retain its security if opened in 2003?

Any advice is greatly appreciated. Thank you for your time and input.