Senior Security Engineer, Sybil Attack Mitigation

Senior Security Engineer, Sybil Attack Mitigation at LMArena

Location: SF Bay Area/Remote

Type: Full-Time

About the Role:

LMArena is seeking an experienced Security Engineer to lead the design and implementation of systems to fight off bots via realtime and post-processing systems. In this role, you’ll be responsible for safeguarding the systems that power real-time AI evaluation, with a particular focus on detecting and mitigating Sybil attacks and other forms of adversarial manipulation. Your work will ensure Arena remains a trusted and resilient platform for the users, developers, researchers, and organizations relying on transparent, community-driven AI benchmarks. This role is ideal for someone who thinks like a builder and a breaker—someone who thrives on identifying attack surfaces, designing resilient defenses, and building systems that scale trust across a growing platform.

Responsibilities:

• Design and implement robust security frameworks to protect against Sybil attacks and other vulnerabilities in distributed systems.

• Conduct threat modeling and risk assessments to identify potential attack vectors, with a focus on Sybil resistance.

• Collaborate with the engineering team to design and implement Sybil-resistant protocols and mechanisms, such as reputation systems, proof-of-work/proof-of-stake mechanisms, or identity verification systems.

• Develop tools and systems to monitor, detect, and respond to Sybil attacks and other security threats in real time.

• Stay up-to-date with the latest research and advancements in Sybil attack mitigation, distributed systems security, and cryptographic techniques. Apply cutting-edge solutions to our platform.

• Work closely with product managers, engineers, and other stakeholders to ensure security is embedded into the product development lifecycle.

• Lead incident response efforts in the event of a security breach or attack, including root cause analysis and remediation.

• Educate the team on security best practices and foster a culture of security awareness across the organization.

• Develop and maintain a comprehensive threat model, including:
  

  • Identification of Sybil attack vectors such as vote spamming, leaderboard manipulation, and collusion

  • Categorization of adversarial behaviors (e.g., botnets, automation, proxy/VPN abuse, human-assisted fraud)

  • Risk assessment for each attack type with severity ratings and projected impact

  • Clearly defined mitigation strategies, detection mechanisms, and response protocols for each category

Who is LMArena?

Created by researchers from UC Berkeley’s SkyLab, LMArena is an open platform where everyone can easily access, explore and interact with the world’s leading AI models. By comparing them side by side and casting votes for the better response, the community helps shape a public leaderboard, making AI progress more transparent, and grounded in real-world usage.

Why Join Us?

Trusted by organizations like Google, OpenAI, Meta, xAI, and more, LMArena is rapidly becoming essential infrastructure for transparent, human-centered AI evaluation at scale. With over one million monthly users and growing developer adoption, our impact is helping guide the next generation of safe, aligned AI systems—grounded in open access and collective feedback.

Our work is regularly referenced by industry leaders pushing the frontier of safe and reliable AI. Sundar Pichai, Jeff Dean, Elon Musk, and Sam Altman.

• High Impact: Your work will be used daily by the world’s most advanced AI labs.

• Global Reach: Develop data infrastructure powering millions of real-world evaluations, influencing AI reliability across industries at the top-tier

• Exceptional Team: We are a small team of top talent from Google, DeepMind, Discord, Vercel, UC Berkeley, and Stanford.

Requirements:

• 5+ years of experience in software engineering or security engineering, with a focus on building secure, scalable systems

• Proven experience designing and deploying infrastructure security measures across cloud environments, identity systems, and access controls

• Hands-on experience implementing user fingerprinting techniques, identity modeling, or behavioral analytics to prevent fraud or abuse

• Experience designing and/or defending against Sybil attacks, bot activity, or adversarial manipulation at the platform level

• Strong knowledge of threat modeling, risk assessment, and designing mitigation strategies for real-world attack scenarios

• Familiarity with common security tools and practices, including VPNs, MFA/2FA, intrusion detection, secrets management, and secure deployment pipelines

• Clear communicator who can collaborate cross-functionally and articulate risks and tradeoffs to technical and non-technical stakeholders

• Bonus: Experience in adversarial ML, trust & safety systems, or securing user-driven platforms with voting or reputation systems

Our Tech Stack:

• NextJS

• Tailwind

• ShadCN

• HonoJS

• Postgres

• Vitest

What we offer:

• 210k - 231k + equity. Actual compensation will depend on job-related knowledge, skills, experience, and candidate location.

• Competitive salary and meaningful equity

• Comprehensive healthcare coverage (medical, dental, vision)

• The opportunity to work on cutting-edge AI with a small, mission-driven team

• A culture that values transparency, trust, and community impact

Come help build the space where anyone can explore and help shape the future of AI.