Abstract: A method and system for approval by a verification computer of an online transaction between a user computer and a merchant computer over the Internet. The user computer transmits a transaction request to the merchant computer, which may include a product to be purchased and the payment amount. The merchant computer transmits to the verification computer a verification request including a first data string associated with the payment card (such as a debit card account number or a portion thereof) and the payment amount. The verification request is stored at the verification computer with a transaction identifier and a verification data string, which are also transmitted to the merchant computer. The merchant computer stores the verification data string as an expected verification data string and the transaction identifier, transmits the transaction identifier to the user computer, and the user computer transmits the transaction identifier to the verification computer.