Written by Modulr | Jul 24, 2025 11:00:00 PM
3D Secure (3DS) is a security protocol designed to add an additional layer of authentication for online credit and debit card transactions. It helps prevent fraud by allowing the card issuer to challenge the cardholder to verify their identity before a payment is authorised. An access control server (ACS) operates within the card issuer's domain, though often outsourced to a third party, to handle the authentication process for 3DS and interacts with the cardholder's browser or mobile app during the authentication phase of a 3DS transaction.