  To prevent password breaches and guessing attacks, banks increasingly turn to
two-factor authentication (2FA), requiring users to present at least one more
factor, such as a one-time password generated by a hardware token or received
via SMS, besides a password. We can expect some solutions -- especially those
adding a token -- to create extra work for users, but little research has
investigated usability, user acceptance, and perceived security of deployed
2FA.
  This paper presents an in-depth study of 2FA usability with 21 UK online
banking customers, 16 of whom had accounts with more than one bank. We
collected a rich set of qualitative and quantitative data through two rounds of
semi-structured interviews, and an authentication diary over an average of 11
days. Our participants reported a wide range of usability issues, especially
with the use of hardware tokens, showing that the mental and physical workload
involved shapes how they use online banking. Key targets for improvements are
(i) the reduction in the number of authentication steps, and (ii) removing
features that do not add any security but negatively affect the user
experience.
