By placing an order with a merchant using either a Buy Button or a Shopping Cart Order, Eve[1] can copy the URL with the XML encoded document and store it to her local machine. She edits the URL, changing the amount of the transaction to a lower amount, and then pastes this URL back into her web browser and executes the redirect. The transaction proceeds as normal. If the merchant does not validate the total amount of the transaction against the shopping cart or catalog value before fulfilling the order, Eve has effectively marked down the price of her purchase without the merchant’s knowledge.
If the merchant does notice that the amount is incorrect and does not fulfill the order, there are three possible scenarios:
[1] When discussing security, it is common to describe various scenarios for analysis. In these scenarios, a malefactor trying to break into a system or compromise its security or integrity is often personified by the name "Eve." With apologies to all people named Eve who are honest, well-intentioned and honourable people, this paper will continue with this tradition.