Security engineer, application security (UK)

🚀 ABOUT WRITER WRITER is the AI platform built for the world’s most ambitious marketing and revenue teams, bringing the frontier of AI to the people who drive enterprise growth. With WRITER, autonomous agents work across the buyer journey, continuously executing on market signals and enterprise intelligence to grow revenue faster. Every agent action and asset is grounded in trust, built on an Enterprise Brain that unites brand, product, and company knowledge with fiduciary-grade governance and compliance. Fortune 500 companies are transforming how they go to market with WRITER, including 3 of the top 5 US banks, 2 of the 5 largest global CPG conglomerates, and 4 of the top 5 US healthcare insurers. Founded in 2020, WRITER is backed by investors including Insight Partners, ICONIQ, Radical Ventures, Premji Invest, Balderton, B Capital, Salesforce Ventures, Adobe Ventures, Accenture, Citi Ventures, IBM Ventures, WndrCo, and others. Learn more at WRITER.com http://WRITER.com. 📐 ABOUT THE ROLE This is where security meets innovation at enterprise scale. As a security engineer, applications at WRITER, you'll be building the security foundations that protect the AI systems powering some of the world's most recognizable brands. You'll work at the intersection of application security, AI infrastructure, and developer enablement—partnering with engineering teams to embed security into every line of code while ensuring our platform remains both powerful and trustworthy. The opportunity is massive: you'll help define how enterprise AI applications are secured, from threat modeling our LLM architectures to building automated security controls that scale across our growing platform. This isn't about saying "no"—it's about finding creative ways to say "yes, and here's how we do it securely." You'll tackle challenges that most security engineers never encounter: securing AI agents, protecting training data pipelines, and designing controls for systems that didn't exist a few years ago. This role is hybrid from our London office, reporting to the head of security engineering. 🦸🏻‍♀️ WHAT YOU'LL DO - Build security into the DNA of our AI platform by conducting threat modeling sessions with product teams, designing secure architectures for new features, and ensuring security considerations shape product decisions from day one—not after the fact - Own and evolve our application security program including establish and maintain SAST/DAST scanning in CI/CD pipelines, conducting security code reviews for critical changes, and building automation that catches vulnerabilities before they reach production - Partner with engineering teams to establish and champion secure coding standards, creating reusable security patterns and libraries that make it easier for developers to build securely by default - Design and recommend security features and products that help secure customer environments. You are the advocate and the vision for how we protect and secure customers.. - Integrate and leverage AI agents to help increase velocity for the security team and the overarching engineering org to ensure that we are proactive in minimizing risk while we build products - Lead security assessments and penetration testing of WRITER's applications, AI services, and APIs, identifying vulnerabilities across our tech stack and working collaboratively with teams to remediate issues at scale - Design and implement security controls for protecting data pipelines, model training environments, and customer-facing AI agents - Stay ahead of emerging threats in the AI/ML security landscape, researching attack vectors specific to LLMs and generative AI, and proactively building defenses against novel risks ⭐️ WHAT YOU NEED - 4+ years of hands-on experience in application security engineering, with a proven track record of securing large-scale production systems—bonus points if you've worked in fast-growing startups or high-growth environ