[FX.php List] How to handle security on web forms that are used more than once?

[Malcolm Fitzgerald]

I have a client who has a rather long application form they want to put onto the web. The applicants are not expected to have all the information required to complete the form. They may need a long time (days) to gather the information. When they return to the web site they should be able to return to their form. All that seems straightforward but the security issues are not. What is the best way to handle this? 

Malcolm