Technical Fraud Specialist

Kleinanzeigen reaches 36M+ monthly users and is Germany’s leading online classifieds market. We are a sustainability-focused platform where you won't just write code; you will power the services that bridge our high-traffic backend with seamless user experiences.

We are looking for a technical fraud analyst to join our growing fraud team. You’ll work at the intersection of data, product, engineering, and CS. Using your analytical and technical skills, you will identify fraudulent behaviour, monitor for credential stuffing attacks, bot attacks, build pro-active rule based defenses, and influence the roadmap to keep Kleinanzeigen safe marketplace.

This is a hybrid role, based in Barcelona Spain.

What you’ll do:

• Analyze fraud patterns using marketplace and behavioral data to uncover new attack vectors, emerging threats, and operational gaps.

• Monitor and respond to credential stuffing attacks, leveraging signals from login, IPs, device fingerprinting, and rate limiting systems.

• Design and implement technical fraud rules, filters, and tools in collaboration with engineering to align fraud prevention efforts and resolve complex incidents.

• Contribute to the strategic fraud prevention roadmap by identifying opportunities for improvements and automation.

• Support incident response and post-mortems for major fraud events, ensuring learnings feed into product and policy improvements.

• Stay current on industry fraud trends, and tools, bringing external insights to help us stay ahead of attacks.

Who you are:

• 4+ years of experience in fraud analytics, trust & safety, or a similar technical role in a C2C marketplace or traditional e-commerce environment.

• Strong proficiency in SQL and experience with data analysis tools (Tableau, Python, etc.).

• Familiarity with bot detection, account takeovers, credential stuffing, and other common C2C fraud patterns.

• Experience writing technical rules with rule engines (Threatmetrix, Arkose, Sift, internal-rule based system, etc.)

• Excellent cross-functional communication skills - you can translate technical findings for non-technical audience / stakeholders & vice versa.

• A curious, proactive mindset and a passion for solving complex problems that have real-word impact.

• Profecient with Python for more advanced data analysis & automation

• Experience to authentication, behavioural biometrics, and fraud stemming from user generated content such as ads and messages

We believe that doing great work requires an environment that supports your professional and personal well-being. Here is what you can look forward to:

• Competitive compensation package

• A unique position in an international and dynamic environment

• Opportunity to shape the way we work. Your feedback and opinions are valued at all levels of the organization

• The chance to be a key player in a growing, highly skilled team

• Great colleagues and a healthy working environment

• Benefits like private health insurance.

• Career development, including individual training budget.

• Flexible benefits program (transport, restaurants, child-care, etc)

• 26 days of holidays