Duo Security, now part of Cisco, leads in multi-factor authentication (MFA) and secure access solutions. Combining the Most Loved Company in Security with the global leader in network technology, Duo aims to democratize security by making it accessible and effective for everyone. As a Machine Learning Engineer on Duo's ML Infrastructure team, you'll design and build systems to manage ML-powered applications. Your role involves collaborating with Data Science & Engineering teams to develop new data-powered products, enhancing Duo’s Zero Trust offering. This guide will help you navigate the interview process for this exciting opportunity. Explore commonly asked questions and valuable tips to succeed in your Duo Security interview journey.

Submitting Your Application

The first step is to submit a compelling application that reflects your technical skills and interest in joining Duo Security as a Machine Learning Engineer. Whether you were contacted by a Duo Security recruiter or have taken the initiative yourself, carefully review the job description and tailor your CV according to the prerequisites.

Tailoring your CV may include identifying specific keywords that the hiring manager might use to filter resumes and crafting a targeted cover letter. Furthermore, don’t forget to highlight relevant skills and mention your work experiences.

Recruiter/Hiring Manager Call Screening

If your CV happens to be among the shortlisted few, a recruiter from the Duo Security Talent Acquisition Team will make contact and verify key details like your experiences and skill level. Behavioral questions may also be a part of the screening process.

In some cases, the Duo Security hiring manager stays present during the screening round to answer your queries about the role and the company itself. They may also indulge in surface-level technical and behavioral discussions.

The whole recruiter call should take about 30 minutes.

Technical Virtual Interview

Successfully navigating the recruiter round will present you with an invitation for the technical screening round. Technical screening for the Duo Security Machine Learning Engineer role usually is conducted through virtual means, including video conference and screen sharing. Questions in this 1-hour long interview stage may revolve around Duo Security’s machine learning infrastructure, data processing pipelines, and Python development.

In the case of ML roles, take-home assignments regarding model development, feature engineering, and system design may be incorporated. Apart from these, your proficiency with cloud infrastructures, large language models (LLMs), and Kubernetes might be assessed during the round.

Depending on the seniority of the position, case studies and similar real-scenario problems may also be assigned.

Onsite Interview Rounds

Followed by a second recruiter call outlining the next stage, you’ll be invited to attend the onsite interview loop. Multiple interview rounds, varying with the role, will be conducted during your day at the Duo Security office. Your technical prowess, including programming and ML modeling capabilities, will be evaluated against the finalized candidates throughout these interviews.

If you were assigned take-home exercises, a presentation round may also await you during the onsite interview for the Machine Learning Engineer role at Duo Security.

Quick Tips For Duo Security Machine Learning Engineer Interviews

• Understand Duo Security’s Product: Being familiar with Duo's product offerings and its impact on cybersecurity will be beneficial. Know how MFA and Zero Trust models work, as these are core to Duo Security's solutions.
• Stay Updated in ML Trends: Duo Security values innovation. Make sure you are updated on the latest trends and technologies within machine learning, especially around LLMs and cloud-based ML infrastructure.
• Prepare for Behavioral Questions: Duo Security promotes a collaborative culture and values diversity in backgrounds and thoughts. Prepare to answer questions that reflect how you fit into Duo’s mission and culture.

Typically, interviews at Duo Security vary by role and team, but commonly Machine Learning Engineer interviews follow a fairly standardized process across these question topics.

• Create a function is_subsequence to determine if one string is a subsequence of another. Given two strings, string1 and string2, write a function is_subsequence to find out if string1 is a subsequence of string2.

• Implement a SinglyLinkedList class with methods to manipulate the list. Create a class SinglyLinkedList with methods to add and remove elements from the head and tail, check for item existence, access elements by index, and get the list's length.

• Write a function swap_node to swap nodes at given positions in a singly linked list. Given the head of a singly linked list and two positions x and y, write a function swap_node to swap the nodes at these positions using pointer manipulation, not by swapping values.

• Would a logistic model still be valid if a variable's decimal points were removed? Assume a logistic model is heavily weighted on one variable, and due to a data quality issue, some values had their decimal points removed (e.g., 100.00 turned into 10000). Would the model still be valid? Why or why not? How would you fix the model?

• How would you design a system to minimize missing or wrong orders on DoorDash? As a data scientist at DoorDash, you need to build a machine learning system to minimize missing or wrong orders placed on the app. How would you go about designing this system?

• What is the relationship between PCA and K-means clustering? Explain the relationship between Principal Component Analysis (PCA) and K-means clustering.

• How would you classify posts by topic on a large-scale social media website? You work at a social media website and want to build a system to automatically detect the topic of new posts. Given the scale of several thousand posts created every hour, how would you create a machine learning model to classify posts by topic?

• What are kernel methods in machine learning, and what are the requirements for a matrix to represent a kernel?

• What are kernel methods in machine learning?
• What are the requirements for a matrix to represent a kernel?
• What happens if we run a support vector machine model using a kernel that does not satisfy these requirements?

What is the average salary for a Machine Learning Engineer at Duo Security?

Q: What makes Duo Security a unique place to work as a Machine Learning Engineer?
Duo Security, part of Cisco, marries the innovative culture of a start-up with the resources and stability of a global leader in network technology. Our mission is to democratize security by designing simple solutions for complex problems. We value diversity, foster a healthy work-life balance, and invest in the continuous learning and growth of our team members.

Q: What are the primary responsibilities of a Machine Learning Engineer at Duo Security?
As a Machine Learning Engineer on the Duo Security ML Infrastructure team, you will design and build systems for our ML-powered applications. Responsibilities include collaborating with various teams to develop new data-powered products, focusing on large language models, and extending our machine learning infrastructure capabilities.

Q: What experience is required for the Machine Learning Engineer position at Duo Security?
Candidates should have at least 2+ years of professional Python development experience, production experience with LLM-based systems, and experience designing stateful cloud infrastructure. Preferred experience includes familiarity with Spark, Delta Lake, or Athena, AWS and Terraform, as well as Kubernetes.

Q: How does Duo Security support employee growth and work-life balance?
At Duo Security, we believe impactful work is rewarding work. We foster collaboration, encourage continuous learning, and recognize hard work. We champion a healthy work-life balance through flexible work arrangements and various wellbeing initiatives.

Q: What steps can I take to prepare for an interview at Duo Security?
To prepare for an interview at Duo Security, research the company’s mission and values, practice common interview questions with Interview Query, and review your technical skills, especially in Python and cloud infrastructure. Be ready to discuss your past experiences and how they align with the responsibilities of the role.

By joining Duo Security as a Machine Learning Engineer, you will be stepping into a dynamic role that blends innovation with impactful work to tackle some of the world’s most critical security challenges. Duo, in partnership with Cisco, is on the cutting edge of secure access solutions and is dedicated to fostering a diverse, inclusive, and collaborative environment. As you work with advanced technologies like large language models and cloud infrastructure, you'll be surrounded by passionate teams that invest in growth, learning, and a healthy work-life balance. Ready to make a real difference in the realm of security? Explore more opportunities and prepare thoroughly with the Duo Security Interview Guide on Interview Query. Your future at the intersection of innovation and security awaits! Good luck with your interview!