Macro with an end date

[backyardfun]

I am currently using the following at the beginning of a macro to give it an end date. However, this can be easily manipulated by changing the computer's system date. Is there a way to make it where the system date will not matter? Thank you!

Dim exdate As Date
    exdate = "5/31/2015"
    If Date > exdate Then
        MsgBox ("MESSAGE")
        ActiveWorkbook.Close False
        End If