If you are on Windows NT you can use the NT login as a security check
eg
Sub AUTO_OPEN
USER = Environ("Username")
If USER <> .... THEN
MSGBOX "You Do Not Have Access Rights to This File",vbcritical,"NO ACCESS"
ActiveWorkbook.Close SaveChanges = True
END IF
Environ("Username") is very handy for running auto open macros as you can predetermine external queries and reports etc on the user basis (i.e. by dept) without requiring any interaction by the user. Unless they know how to log on as someone else it's also pretty safe.