Personal firewalls are an important aspect of security for home computer users, but little attention has been given to their usability. We conducted semi-structured interviews to understand participants’ knowledge, requirements, expectations, and misconceptions for personal firewalls. Analysis of 10 interviews shows that different design decisions (i.e., level of automation, multiple profile settings) are appropriate for users with different levels of security knowledge and experience. Keywords Usable security, personal firewall. ACM Classification Keywords H.5.2 Information Interfaces and Presentation: User Interfaces-User-centered design; D.4.6 Software: Security and Protection-Information flow controls