A secure payment method and system for payment for a product in electronic form comprises a customer's terminal and a merchant's terminal connected by a communications network. A customer uses a customer's terminal to request a product and at the customer's terminal, it is determined whether the product has previously been paid for by identifying if there is a corresponding transaction receipt stored at the customer's terminal. If there is a corresponding receipt this is transmitted with the request to the merchant's terminal. At the merchant's terminal, when the request is received, if there is an accompanying transaction receipt, the product is transmitted to the customer's terminal. If there is no accompanying transaction receipt, the transaction is recorded and a transaction receipt is generated and transmitted to the customer's terminal. A central server can be provided to aggregate transactions by periodically polling the merchant's terminal to retrieve transaction data and for periodically polling the customer's terminal to retrieve receipt data. The receipt data and the transaction data can be reconciled in order to authenticate transactions.