CISOs point to a catalog of problems emerging as data localization laws continue to spread beyond the 144 measures imposed by 62 countries. Challenges include weakened threat monitoring, fragmented cyber hygiene efforts and internal tensions between privacy, business and cybersecurity teams. This final article in a three-part series on managing data localization laws details consequences for cybersecurity and companies’ possible responses, and includes insight from the chief security officer of Mastercard. Part one explained five varieties of localization laws and surveyed 2021’s enforcement and fines. Part two described several compliance consequences and one international company’s approach to localization. See “Reconciling Data Localization Laws and the Global Flow of Information” (Oct. 11, 2017).