I'm making a module that generates a form in the frontend, and I have a question about the expected behaviour of a form when the browser back button is used.

What happens now is that if I submit the form say 5 times, I can use the browser back button and run through the entire 5 populated forms (therefore seeing all 5 sets of previous submitted data).

I take it this is not supposed to happen, as person b on a computer could potentially see persons a's data.

Does anyone know how I would prevent this - that is make the data irretrievable after submission?
Or is this perfectly acceptable behaviour as far as forms are concerned?