Developer finds his spam filter was leaking its own bypass instructions to attackers

Ronny Cruz Alvarez, founder of Open Feed Network, discovered a critical design flaw in Sentinel, his spam-detection engine, while building a registration filter during a July Fediverse spam wave. The system was returning detailed rejection messages that included the exact regex patterns used to flag spam, effectively giving bad actors a roadmap to evade detection. Although nothing was technically broken, the engine was silently exposing its own logic to anyone who received a rejection response. Cruz fixed the issue the same day by separating internal detection reasoning from public-facing responses, ensuring external messages use only generic, non-specific language. The incident led him to establish a core rule for Sentinel: detection logic and detection disclosure must always be treated as two distinct systems.