Open Source Software (OSS) is a relatively new and evolutionary process of producing software based products and firms incorporate them in their market offers through different approaches and create appealing offers to compete. This work focuses on the vertical market that has been established across Open Source Security related projects that are named Open Source Security Tools (OSST). An empirically derived quantitative study of 184 firms active in the Open Source Security context is presented in this book. Exploratory Factor Analysis techniques are used to extract nine types of market offers using information from the Internet and public websites of the firms. Five of these offer types are unique to OSST and the security concept of OSS: (i) Security Analysis Services; (ii) Monitoring Services; (iii) Confidentiality services; (iv) Authentication, Authorization, and Accountability Services; and (v) Disaster Recovery and Business Continuity Services. Not only this work identified different market offers by OSS and OSST, but also it provides a reference for doing quantitative study on publicly available data by using keywords search.