Do not probe others websites for vulnerabilities without permission. Cross-site request forgery (XSRF) and client state manipulation (XSS) are examples of XSS vulnerabilities. You can learn how to find vulnerabilities in your own web app and how to fix them in the second part of Gruyere ; or, if youre an advanced developer, take a look at the automatic escaping features in template systems we blogged about previously on this blog.Protecting your application against this kind of attack is not easy; learn a few tips about how to defend your app.”]
Source: https://security.googleblog.com/2011/05/website-security-for-webmasters.html