Security is a subset of quality. Security must be built in, because adding it in later is costly and will likely not provide very good security. A bug in any part of the application may be a security vulnerability, so everyone is responsible for writing secure code.
The Chandler security project encompasses everything from identifying security threats we need to protect against and technologies we will use to counter the threats: cryptography, access control and secure software development methodologies and best practices. We also lump privacy with security. Finally there is a policy and plan for security response when things go wrong.