Hi Jam,
Unfortunately Excel can be easily crack, nothing you can do

" wrote:

Hi
I want to protect a workbook that contains may sheets, some sheets
should be invisibles, others with some cells that contains formulae
should be protected and invisible. I of course use the preotection and
hide tools in excel, but ther are many freeware that crack the excel
password, is there any hint to do more secure and stronger password.
Thanks in Advance
Jam