Protect Workbook From Editing / Viewing

I have placed a workbook on a network drive. This workbook contains sensitive information and I would like to protect it to a "feasible" degree. I have written the following code

Private Sub Workbook_Open()
Dim userid As String, valid_userid As String
Dim i As Integer
valid_userid = "MISI01/"
userid = GetUserName()
userid = UCase(userid) & "/"
i = InStr(1, userid, valid_userid)
If i = 0 Then
MsgBox ("You are not authorised to use this workbook")
ActiveWorkbook.Close False
Exit Sub
End If
'create menu when workbook opens
Call Module1.CreateMenu("")
Call Modul1.check_filedate("")
' This will disable the user from moving, renaming etc the sheets
ActiveWorkbook.Protect Structure:=True, Windows:=False
End Sub

As can be seen from the above code, I check if the current userid is one of those that are valid to open the workbook. If not the idea is to tell them and close the workbook immediately (this bit isn't tested yet). This code is not supposed to be hacker proof, but to prohibit the casual user from reviewing the the data.