Anno --
Actually it's possible to decrease the success of that paste link formula approach by encrypting the source file data through a VB application. Or, for a simpler workaround, save the file as a blank template in a dummy file path, or keep it stored in an undisclosed path.
I agree with the premise of your follow-up: no such thing as absolute security.
Rumor has it that Thomas Jefferson's actual quote was, "The price of Excel mastery is eternal vigilance."