Pro PHP Security: From Application Security Principles to the Implementation of XSS Defenses, Second Edition

Identity Verification

The problem of identity verification (in other words, verifying that someone is who they say they are) is particularly difficult for online communities, since they typically have a large and geographically diverse user base. The problem is exacerbated for applications that allow new users to register via a public form. This makes it impractical to research the identity of each individual applicant before granting access. Abusers can remain essentially anonymous. Furthermore, a single problem user can, with a little work and the use of anonymizing proxies, or botnets(networks of robot machines, engaging in automated attempts at various kinds of attacks; see http://en.wikipedia.org/wiki/Botnet for more information), register ...