I want a dialog box when opened
 

I want a dialog box to appear when the excel file is opened. It would contain
a warning of "protected" information and all the user would have to do is
click "OK' and then the spreadsheet would open. How do I do this?

I want a dialog box when opened
 

press Alt+F11
in ThisWorkbook module insert the following

Private Sub Workbook_Open()
MsgBox "Protected information." & vbcrlf & vbcrlf & "Click OK to
continue"
End Sub