Senior Software Engineer, Security

Flex · Remote / USARemotesenior

In short

▸Ingeniero de software de seguridad senior que construye sistemas autónomos para proteger flujos críticos de dinero.
▸Revisa diseño temprano, automatiza detecciones y prioriza riesgos con impacto real en velocidad y seguridad.
▸Trabajas directamente con el CTO, defines el estándar de seguridad sin equipo de seguridad tradicional.

Fluency in English required

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What they ask for

✓Experiencia sólida como ingeniero de software con enfoque en seguridad
✓Capacidad para construir automatización de seguridad en lugar de revisar manualmente código
✓Comprensión profunda de sistemas críticos como ledgers, emisión de tarjetas y pagos
✓Experiencia en arquitectura de sistemas a gran escala y alta disponibilidad
✓Habilidades de liderazgo técnico para influir sin autoridad formal
✓Capacidad de comunicar riesgos técnicos a equipos de negocio y producto

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Flex is building the AI-native private bank for business owners. We’re re-architecting the entire financial system for entrepreneurs—from the first dollar a business earns to how that value compounds, moves, and is ultimately spent in real life. Banking, credit, payments, personal finance, and financial operations—rebuilt from the ground up as a single, intelligent system. Flex is the full financial home for ambitious owners. Since launching publicly in September 2023, Flex has scaled from zero to nine-figure annualized revenue, with a clear path to profitability by late 2026. We move fast, ship relentlessly, and operate with extreme ownership. Our customers are affluent business owners ($3–$200M in revenue)—the backbone of the economy and one of the most underserved segments in finance. They’re stuck with outdated banks and fragmented tools. We’re replacing all of it. The opportunity is massive: a ~$1T+ revenue market hiding in plain sight. Our ambition is to build a $100B+ company by delivering a product that is fundamentally better—not incrementally improved. Flex has raised $100M+ in equity and $300M+ in debt. - Mission-critical problems: We build software that directly controls how money moves at scale. - High bar, low ego: Small teams, exceptional people, real ownership. - Speed over comfort: We prioritize execution, quality, clarity, and results. - Enduring impact: What we’re building will define how a generation of owners runs their businesses. Team & Locations We hire exceptional people who want to build hard things and see their work matter immediately. Roles are available in: San Francisco, Miami, New York, and fully remote. Flex Fuels Ambition. About the Role We're hiring our first security engineers. Both report directly to the CTO. We want software engineers with security as their superpower, not security specialists who occasionally write code. The distinction matters here. At our size, the only way one person covers a surface this large is to build things that keep working after they move on. A findings queue you work through by hand grows faster than you can close it. A guardrail in the deployment pipeline doesn't. The work is product and infrastructure security: making the paths that move money hard to attack, and making the secure way to build something also the easy way. The ledger and its write path, card issuing, payouts, and our stablecoin work are the systems that matter most. The job runs in both directions. You'll be in design review early on anything new, and you'll be continuously assessing what we've already shipped, because most of Flex's risk lives in code that exists today. We don't expect you to read the codebase by hand or to keep a findings queue. We expect you to build the automation and repeatable checks that keep assessing it for you, and to spend the time you get back on the golden paths that stop whole classes of problem from arriving again. There's no security team above you and no CISO. You'd set the standard here, and own the risk decisions that come with it. Day to day, what gets fixed now, what gets mitigated, and what we knowingly accept is your call. The large ones come to the CTO, who you report to directly and who'll back you when the answer is no. Corporate security posture, endpoints, and identity sit with our IT and Corporate Engineering function, and those decisions are theirs to make. At a company shipping this fast, a security engineer who blocks everything is worse than no security engineer. The answer isn't to wave things through. It's to understand the system, the business context, and the actual risk well enough to find the mitigation that keeps the velocity. Sometimes the answer is still no, and we'd want that to come from a real read of the risk rather than a standard applied by default. Getting engineers to adopt something matters here as much as finding the problem in the first place. The version of this job that works has Security and Engineering solvi

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