What is the most secure form of code testing and review?

While open-source code can benefit from community review, it doesn't guarantee the same level of in-depth, targeted security analysis that a dedicated internal team provides for proprietary systems.

Proprietary/internal review can be very thorough but might lack the diverse perspectives and sheer number of eyes that open-source scrutiny can provide, potentially leading to blind spots.

Neither open source nor proprietary alone represents the most secure form; the strengths of each are complementary.

A combination of open source and proprietary/internal code testing and review is generally considered the most secure because it benefits from both broad community scrutiny and specialized internal expertise. Open-source models allow a vast community to review code for vulnerabilities (Linus's Law), while proprietary internal review can focus on specific business logic, intellectual property concerns, and deeper, context-specific testing. This dual approach maximizes the chances of discovering vulnerabilities and ensuring robust security.