Comments on a Dynamic-ID-Based Remote User Authentication Scheme for Multi-server Environment Using Smart Cards

User authentication prevents unauthorized users from accessing resources or getting applications illegally. Due to the rapid development of computer network technologies, users may gain the desired services in a multi-server environment. Recently, Lee et al. proposed a dynamic-ID-based remote user authentication scheme for multi-server environment using smart cards. They adopt dynamic ID to provide user anonymity. However, we found that their scheme suffers from some security drawbacks. in this paper, we show the perceived security drawbacks in detail and give some helpful remedy recommendations.