Every big online security breach seems to end in a big lecture. Thus, although a predominant weakness in properly securing information assets is the individual user within an organization, much of the focus of extant security research is on technical issues. The purpose of this study is to explain why insiders breach security policy by applying the moral disengagement theory. There are no consistent, widely accepted theories or theoretical frameworks in the literatures as to why insiders breach of information security, and therefore no clear, effective guidance on what to do to prevent employees from violating information security policy in organization. To do this, we theorize that moral disengagement may play a mediating role connecting stable individual differences to intention to breach security policy, because of some of the individual differences. We found that policy awareness and perceived punishment have a negatively significant effect on moral disengagement. However, negative affectivity has a positively significant influence on moral disengagement. Furthermore, moral disengagement has a positive effect on intention to breach security policy. Conclusions and implications are discussed.