Devon is writing the following code to avoid what?

<script language="vb" runat="server">

Sub Application_BeginRequest(Sender as object, E as EventArgs)

If (Request.Path.Indexof(chr(92)) >= 0 OR _

System.IO.Path.GetFullPath

(Request.PhysicalPath) <> Request.PhysicalPath)

then

Throw New HttpException(404, "Not Found"

End If

End Sub

</script>