Computer technologies that protect data and systems from viruses, unauthorized access, disruptions, spyware and other threats have become increasingly important in the globally networked economy and society. Yet little is known about user attitudes and behaviour towards this category of information technologies. Comparative studies across different cultures in this context are even rarer. In this study, we examine the cross-cultural differences between South Korea and the United States in user behaviour towards protective information technologies. We develop a theoretical model of user behaviour based on the framework of the theory of planned behaviour and national cultural dimensions and indices. We posit that cultural factors moderate the strength of the relationships in the behavioural model in the context of protective information technologies. The model was then empirically tested using structural equation modelling techniques in conjunction with multi-group analysis. Most of the hypothesized moderating effects of national cultural factors were found to be statistically significant. Our findings suggest that cultural factors should be considered in order to design effective information security policies, practices and technologies in global networks where multiple cultures coexist. Theoretical and practical implications of the study are discussed.