The objective of this paper is to study how a software product company can expand its productbased business with the Software as a Service (SaaS) model into the mobile setting. We focus on a mobile security as a service offering and examine how the SaaS model can be implemented by a software company with existing PC-based software business. The differences between the product and service business are considerable and the change of focus from one to the other is not easily done. In order to create successful and sustainable business, the SaaS model tries to bridge the gap between the software product and service business. Our findings include that by successfully solving the challenges associated with the SaaS model and by taking advantage of the benefits, the case company FSecure, which operates in the virus and intrusion prevention field, managed to leverage its domain area expertise with its SaaS offering. The case company expanded its PC-based antivirus and security application bus...