Falcon - 5:59 pm on Jan 5, 2002 (gmt 0)
Currently, I use the mals-e.com shopping cart. One feature that he has supplied is a simple security check for posting items to his cart. It is a hash value of the item, qty, and price. When he gets the post to add it to the cart, he recomputes the value and checks it against what you posted. I understand there are ways of hacking that but for a low tech, quick fix - he has done a pretty decent job.