The purpose of this study is to explore systems users' behavior on IS under the various circumstances (e.g., email usage and malware threats, online communication at the individual level, and IS usage in organizations). Specifically, the first essay develops a method for analyzing and predicting the impact category of malicious code, particularly email worms. The current study creates two frameworks classifying email worms based on their detrimental impact. The first is the Total Life Impact (TLI) framework, a classifier to categorize worms in terms of their impact. The other is the Short Term Impact (STI) framework which allows for prediction of the impact of the worm utilizing the data available during the early stages in the life of a worm. Given the classification, this study identifies how well the STI framework allows for prediction of the worm into its final impact category. The second essay aims to examine the effects of both spam and the resulting lack of privacy on users' behavior with respect to e-mail usage. This study reveals that spam e-mail triggers users' privacy concerns and, in turn, such concerns influence the way that the users cope with spam or junk mails. Upon receiving spam e-mail, the users predominantly exhibit two different behavioral patterns: usage-oriented (passive) and protection-oriented (proactive) behavior. The third essay examines the impact of perceived information assurance, risk, and resilience on IS effectiveness in the context of extreme events. Resilience in organizations is the positive capacity to cope with negative extreme events. Also, this is critical to ensuring business continuity. While the subject of resilience has been investigated from an engineering perspective, from an IS context, it remains an understudied area. The present study develops a model that is tested with data collected from three of the hospitals in Western New York that were affected by a major snowstorm (labeled a federal disaster). [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]