James Bessen did another study which shows again that software patents harm more than they help. Abstract:
This report examines changes in the patenting behavior of the software industry since the 1990s. It finds that most software firms still do not patent, most software patents are obtained by a few large firms in the software industry or in other industries, and the risk of litigation from software patents continues to increase dramatically. Given these findings, it is hard to conclude that software patents have provided a net social benefit in the software industry.