Multi-Factor Authentication (MFA) enhances login security by requiring multiple authentication factors. Its adoption has increased in response to more frequent and sophisticated attacks. Duo is widely used by organizations including Fortune 500 companies and major educational institutions, yet its usability has not been examined thoroughly or recently. Earlier studies focused on technical challenges during initial deployment but did not measure core usability metrics such as task completion time or System Usability Scale (SUS) scores. These results are also outdated, originating from a time when MFA was less familiar to typical users. We conducted a long-term, large-scale Duo usability study at the University of California Irvine during the 2024-2025 academic year, involving 2559 participants. Our analysis uses authentication log data and a survey of 57 randomly selected users. The average overhead of a Duo Push task is nearly 8 seconds, which participants described as short to moderate. Overhead varies with time of day, field of study, and education level. The rate of authentication failures due to incomplete Duo tasks is 4.35 percent, and 43.86 percent of survey respondents reported at least one Duo login failure. The Duo SUS score is 70, indicating good usability. Participants generally find Duo easy to use but somewhat annoying, while also reporting an increased sense of account security. They also described common issues and offered suggestions for improvement.

翻译：多因素认证（MFA）通过要求提供多种认证因素来增强登录安全性。随着攻击日益频繁和复杂，其采用率不断提高。Duo被包括《财富》500强企业和主要教育机构在内的组织广泛使用，但其可用性尚未得到全面或近期的检验。早期研究主要关注初始部署阶段的技术挑战，并未测量核心可用性指标，如任务完成时间或系统可用性量表（SUS）得分。这些结果也已过时，源于普通用户对MFA尚不熟悉的时期。我们在2024-2025学年于加州大学欧文分校开展了一项长期、大规模的Duo可用性研究，涉及2559名参与者。我们的分析使用认证日志数据以及对57名随机选取用户的调查。Duo推送任务的平均开销接近8秒，参与者描述其为短至中等时长。开销随一天中的时间、研究领域和教育水平而变化。因未完成Duo任务导致的认证失败率为4.35%，且43.86%的受访者报告至少经历过一次Duo登录失败。Duo的SUS得分为70，表明其可用性良好。参与者普遍认为Duo易于使用但略显烦人，同时也表示账户安全感有所提升。他们还描述了常见问题并提出了改进建议。