passing data from one controller function to another

[eluser]newtonianb[/eluser]
this is great, thanks!
do i need do add some validation to the data as it gets to the new function if it is stored in flash data? Is it easy for someone to tamper the data or is it stored on server.

My ideal situation is if the data is stored on server and never on client so they have no way to temper with it.