Cross Site Request Forging (see
http://en.wikipedia.org/wiki/Cross-site_request_forgery for more information) has been around for a while now. It misuses the trust of a web application that every request sent by the browser is wanted by its user.
For example, if you know that i am logged in to our blog admin backend most of the time, and you know its url and software, you could trick me into visiting a special prepared url. That url contains a small javascript that automatically submits a fake form to our admin backend, and short time later everybody is surprised to read on our blog that Mayflower will leave the domain of web application development and open a butcher's shop instead.
Since the authors of our blog software are smart people, they implemented a CSRF protection. And not only them, even we not as smart PHProjekt developers implemented one.
There are three popular ways to protect your software against CSRF: