Hide without possibility of unhiding from Excel UI:
ActiveSheet.Visible = xlSheetVeryHidden
Probably in VBScript it will be ActiveSheet.Visible = 2
EDIT:
After added clarification in comment:
I think the only way to achieve it will be to add on Activate
event code to hide it always and protect VBA project by password. Something like below.
Private Sub Worksheet_Activate()
ActiveSheet.Visible = xlVeryHidden
End Sub
Then you can add Sub or Function to unhide this sheet with hard-coded password (password will be passed as argument and verified against hard-coded string). In this Sub you can set some global variable to bypass Activate
logic.
Then unhiding from VBA Immediate window will also not work. In BeforeSave
event you can hide this sheet to have it always hidden for other users.
Not sure if this fullfils your needs but I think it will be hard to achieve more.