With the diffusion of ubiquitous technologies, many city facilities that are closely related with our daily life are being combined with IT technologies. As a result, various IT services running on the separate network are also being integrated into a city-based service. However, serious problems can occur in terms of the stability and reliability of the u-City (Ubiquitous City )service, if the security factor is not fully considered and applied while developing new IT services that will be integrated into u-City projects. In particular, if any security incident occurs at the u-City Integrated Operation Center (uCIOC), which is designed to collect, analyze and combine the city-related information, and manage and operate the city functions, serious chaos could occur due to a paralysis of the city functions. This paper analyzes the characteristics and security threats against uCIOC, and proposes measures to protect against or counter these threats.