The granting of computer program and electronic business method patents has raised doubts and concerns among researchers in economics and among supporters of open source software. The patent systems in the US and in Europe and their economic impacts are different and have been analyzed in recent studies. The following work is intended to highlight the current set of knowledge on the economic impact of software patents in the United States and Europe and the impact that the less permissive European system has on the diffusion and use of open source software. In this work a brief evolution of the software industry is presented. Scientific papers that analyze empirically the questions of software patent quality and the impact on the innovative activity caused by such patents are reported. The main theories on the economic motives of open source software are studied and reviewed in light of recent changes to the economic system. Lastly the industry and economic effect of the diffusion of open source software in Europe and the problems with computer implemented inventions patents are evaluated.