The same-origin policy is a very important security concept in terms of user interaction within a website or application. Without the implementation of the same-origin policy, arbitrary sites loaded within an iframe would not only be able to access the DOM of the parent site, but also its cookies and form data.

Modern browsers do a good job of implementing the same-origin policy to prevent this from happening in social application development, but some older browsers do not take adequate measures to restrict sites from violating the policy.

While these older browsers are by no means a large majority of those currently in use, these insecurities should still be noted.