The Open Source Vulnerabilty DataBase provides accurate, detailed, current and unbiased technical information regarding security vulnerabilities.

The Institute for Security and Open Methodologies provides a myriad of open source resources for security practitioners.

The Center for Internet Security is a not-for-profit cooperative organization providing benchmarks for best global security practices.

The Sardonix Security Portal promotes Open Source application security by auditing and patching existing applications.

Top 75 Security Tools Fyodor's list of most used Open Source security tools.