As the popularity of the web increases and web applications become tools of everyday use, the role of web security has been gaining importance as well. The last years have shown a significant increase in the number of web-based attacks. For example, there has been extensive press coverage of recent security incidences involving the loss of sensitive credit card information belonging to millions of customers. Many web application security vulnerabilities result from generic input validation problems. Examples of such vulnerabilities are SQL injection and Cross-Site Scripting (XSS). Although the majority of web vulnerabilities are easy to understand and to avoid, many web developers are, unfortunately, not security-aware. As a result, there exist many web sites on the Internet that are vulnerable. This paper demonstrates how easy it is for attackers to automatically discover and exploit application-level vulnerabilities in a large number of web applications. To this end, we developed Se...