Understanding users’ individual differences may provide clues to help identify computer users who are prone to act insecurely. We examine factors that impact users’ reported security behaviour with respect to some common computer security issues. We conducted two online surveys with a total of 650 participants to investigate the relationship between self-reported security behaviour and users’ knowledge, motivation, confidence, risk propensity, and sex-typed characteristics. We found that all of these factors had an impact on security behaviour; however, knowledge was the most important. We provide recommendations relating to understanding participants’ individual differences as a way to identify users at risk of behaving in an insecure manner. Further, we suggest that deeper understanding of the relationships between personality characteristics and security behaviour can provide researchers with tools to more comprehensively interpret their data.