Open source software has publicly available source code that anyone can inspect, audit, and modify. In the context of privacy tools, open source matters because it allows independent verification of security claims.
A VPN claiming no logs with proprietary code cannot be independently verified. An open source VPN can be audited by external researchers, and those audits can be published.
Open source does not automatically mean secure. The value is auditability: independent researchers can find and disclose problems that a company might otherwise conceal.
What it means in practice
Open-source code can be independently audited, which means security researchers and adversaries both have access to it. In practice, widely audited open-source security tools (Signal, Proton, WireGuard, ExifTool) have a better track record than closed-source alternatives because flaws get found and fixed publicly. Closed-source tools may hide vulnerabilities — or backdoors — that are never disclosed. Open source is not a guarantee, but it is a meaningful indicator when combined with regular third-party audits.
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