Unknown to most people sheets have 3 visible states. Visible, Hidden and Very
Hidden. The last one can only be accessed via code or the VBA window. Here
are some simple instructions too make your sheet very hidden.
Right click the Tab you want to hide and select View Code
When the macro screen opens up hit F4 to bring up the Properties Window(if
it is not already on)
The last property for the sheet is the Visible property. Change it from 0 -
xlSheetVsible to 2 - xlSheetVeryHidden
Note whiel this is not entirely foolproof there are no foolproof solutions
in XL. this will keep out 99.9% of people.