New theory of why people forget passwords

Passwords are not hard to remember because they are long, rather human memory forgets them selectively. But how? Our work with Janne Lindqvist’s’ lab at Rutgers presented a new predictive model for which passwords are forgotten. The results were presented at USENIX Security ’18. The paper "Forgetting of Passwords: Ecological Theory and Data" is available at



It is well known that text-based passwords are hard to remember and that users prefer simple (and non-secure) passwords. However, despite extensive research on the topic, no principled account exists for explaining when a password will be forgotten. This paper contributes new data and a set of analyses building on the ecological theory of memory and forgetting. We propose that human memory naturally adapts according to an estimate of how often a password will be needed, such that often used, important passwords are less likely to be forgotten. We derive models for login duration and odds of recall as a function of rate of use and number of uses thus far. The models achieved a root-mean-square error (RMSE) of 1.8 seconds for login duration and 0.09 for recall odds for data collected in a month-long field experiment where fre- quency of password use was controlled. The theory and data shed new light on password management, account usage, password security and memorability.