On the Internet, digitally active small and medium sized enterprises (SME) face numerous security risks. When SMEs join networks, business ideas and malicious activities may interfuse. E-mail marketing, remote control and information gathering are replaced by spam, virulent programs and spyware. In this paper, we use the concepts of information ecosystems to describe a security model where, as a background, humans are presumed to act as Machiavellian beings, i.e., behaving selfishly. Based on this notion, we analyse behaviours initiated by network contaminants and their effects to an entire ecosystem. The contribution of this paper is the security model, which permits a comprehensive view on the risk environment in virtual networks (like the digital SME community).