The World Wide Web has been an environment with many security threats and lots of reported cases of security breaches. Various tools and techniques have been applied in trying to curb this problem, however new attacks continue to plague the Internet. We discuss risks that affect web applications and explain how network-centric and host-centric techniques, as much as they are crucial in an enterprise, lack necessary depth to comprehensively analyze overall application security. The nature of web applications to span a number of servers introduces a new dimension of security requirement that calls for a holistic approach to protect the information asset regardless of its physical or logical separation of modules and tiers. We therefore classify security mechanisms as either infrastructure-centric or application-centric based on what asset is being secured. We then describe requirements for such application-centric security mechanisms.