The principle of least privilege requires that users and their programs be granted the most restrictive set of privileges possible to perform required tasks in order to limit the damages caused by security incidents. Low-privileged user accounts (LUA) and user account control (UAC) in Windows Vista and Windows 7 are two practical implementations of this principle. To be successful, however, users must apply due diligence, use appropriate accounts, and respond correctly to UAC prompts. With a user study and contextual interviews, we investigated the motives, understanding, behaviour, and challenges users face when working with user accounts and the UAC. Our results show that 69% of participants did not apply the UAC approach correctly. All 45 participants used an administrator user account, and 91% were not aware of the benefits of low-privilege user accounts or the risks of high-privilege ones. Their knowledge and experience were limited to the restricted rights of low-privilege accounts. Based on our findings, we offer recommendations to improve the UAC and LUA approaches.