Most security attacks exploit in-stances of well-known classes of implementation flaws. Developers could detect and eliminate many of these flaws before deploying the software, yet these problems persist with disturbing frequency-not be-cause the security community doesn't sufficiently understand them but because techniques for preventing them have not been integrated into the software development process. This article describes an extensible tool that uses lightweight static analysis to detect common security vulnerabilities (including buffer overflows and format string vulnerabilities).