Production fintech security is multi-layered and regulated. PCI DSS requires network segmentation to segregate cardholder data environments, encryption at rest and in transit, role-based access restrictions, and frequent penetration testing against specified attack vectors. Beyond card data security, robust engineering practices include end-to-end encryption for sensitive financial data, RBAC with immutable audit trails for compliance reporting, automated vulnerability scanning in CI/CD pipelines, and SCA enforcement at all authentication points. DORA demands frequent resilience testing for ICT risk scenarios, including cyber events, with supervisory review documentation. AI-assisted code review tools are widely used in development processes to catch security concerns like incorrect key handling or missing input validation before they reach the main branch.