本研究基於雙邊市場理論，探討金融科技（FinTech）發展是否對信用卡網路交易擴張下的詐欺案件產生誘發效果。以2019年至2024年間台灣各縣市（A收單銀行逐筆信用卡交易資料與警政署逐筆詐欺案件資料），按月份統計作為樣本觀測值，運用PPML並結合HDFE進行實證分析。研究結果顯示，網路交易的提升與詐欺案件數呈現顯著正相關，特別於六都地區效果最為明顯。本研究進一步透過穩健性檢定與區域異質性分析，驗證此結果具高度穩定性與解釋力。本實證結果支持雙邊市場理論中「跨端負向外部性」的假說，當網路交易普及（消費端、商戶端增長）將負向外部性地導致犯罪端（詐欺者）活動機會增加，造成整體平台安全風險升高。此外，也補充了既有FinTech文獻中對於網路交易外部性的實證證據不足之缺口。本研究結果之政策意涵，可引導金融機構與主管機關重視強化網路交易身份驗證、多因子認證與即時交易監控之重要性，特別針對高科技密度與高人口流動之都會區，需加強詐欺防制與風險管理機制，以達成推動無現金社會與普惠金融的同時，也同時維護消費者之交易安全。

Motivated by the framework of two-sided market theory, this study investigates whether the expansion of Financial Technology (FinTech) leads to an increase in fraud through the growth of online transactions. Using monthly panel data across Taiwan’s counties and cities from 2019 to 2024, including transaction-level credit card data from a major acquiring bank and fraud case records from the National Police Agency, we employ a (Poisson Pseudo-Maximum Likelihood, PPML) estimation combined with (High-Dimensional Fixed Effects, HDFE) to control for unobserved heterogeneity and distributional characteristics of count data. The empirical findings reveal a significant and robust positive relationship between the proportion of online transactions and the number of reported fraud cases, particularly in metropolitan areas. Robustness tests and heterogeneity analysis further confirm the consistency and explanatory power of the results. These findings support the hypothesis of cross-side negative externalities in two-sided platforms: as online usage by consumers and merchants increases, opportunities for fraudulent actors to exploit the system expand, thereby amplifying systemic security risks. This study also addresses a gap in the FinTech literature by providing empirical evidence on the unintended risks associated with digital payment expansion. Policy implications highlight the need for enhanced digital identity verification, multi-factor authentication, and real-time transaction monitoring, especially in densely populated and technologically advanced urban areas, ensuring that the advancement toward a cashless society and broader financial inclusion does not compromise consumer protection or transaction security.