Techniques are disclosed relating to determining a risk score for domains associated with a transaction. In some embodiments, a transaction computer system receives transaction details for a transaction between a consumer and a merchant, where the transaction details are received from the merchant real-time with the transaction and include a set of transaction URLs for subsequent use in the transaction. The computer system may receive, from a browser of the consumer that is used to initiate the transaction, URL referrer information real-time with the transaction, where the URL referrer information indicates a referring web page to the transaction computer system. The computer system may determine, using the set of transaction URLs and the URL referrer information, a set of domains for the transaction and then determine a risk score for the set of domains. The computer system may determine, based on the risk score, whether to allow the transaction.