Best way to build a wizard with CodeIgniter?

[eluser]parham90[/eluser]
Hi there,

My client requires a sign-up wizard. I originally began implementing it with URI's like:

http://example.com/users/signup/1
and
http://example.com/users/signup/2

It occurs to me that this method is very insecure (E.G. the steps could be modified, tampered with, etc), and I wouldn't have sufficient data to add to the database in the end. So, should I just say that the data is not complete, or make it based on session data (I.E. store the current step in the session)? I have heard that session data also can be modified, so that's why I am not sure whether or not I should trust that one.

Thanks!