Cross-site request forgery (CSRF) is a common and serious exploit where a user is tricked into performing an action he didn’t explicitly intend to do. This can happen when, for example, the user is logged in to one of his favorite websites and proceeds to click a seemingly harmless link. In the background, his profile information is silently updated with an attacker’s e-mail address. The attacker can then use the website’s password reset feature to e-mail herself a new password and she’s just successfully stolen the account.
PHPMaster: Preventing Cross-Site Request Forgeries