This is what happens when large numbers of websites allow a central authority to run arbitrary code within their sites DOM. The central authority becomes an exc

This is what happens when large numbers of websites allow a central authority to run arbitrary code within their sites DOM. The central authority becomes an excellent distribution vector for malware so an extremely lucrative target. People willing to block all cross-origin requests and manually whitelist only those required (Firefox RequestPolicy addon) are the best protected from these problems. NoScript users also get brilliant protection. Even AdBlock users are considerably safer than your average user from this problem.