In the beginning, Intellectual Ventures presented itself as one of the good guys. Founded a decade ago by former Microsoft honcho Nathan Myhrvold, it made the rounds to Silicon Valley's largest tech companies, convincing them to pony up millions of dollars to buy up patents in order to keep them out of the hands of patent trolls. According to Business Week, by 2006, the investors included Microsoft, Apple, Nokia, and eBay.

But as IV's patent arsenal has grown, the tone of Myhrvold's sales pitch has changed. Companies began to wonder if they might become a target of IV's own patents if they declined to sign up. Myhrvold used to emphasize that IV itself hadn't sued anyone, but he refused to rule out doing so in the future. Recently, IV has faced accusations that it set up shell companies like Oasis Research and LodSys so it could engage in patent trolling without leaving fingerprints.

In the last year, IV has dropped any pretenses and started filing lawsuits itself. The latest salvo came on Thursday, when IV sued Motorola Mobility for patent infringement. The complaint names a wide variety of both Android and non-Android phones as infringing six distinct patents. IV says it has been trying to negotiate licensing terms since January, but apparently the firms weren't able to reach an agreement. Ironically, Google, which is acquiring Motorola Mobility, was an early IV investor.

Four of the six patents are software patents. One, filed in 2005, covers the concept of allocating bandwidth on a wireless network "based on contents of packets to be communicated." Another, filed in 2000, appears to cover the concept of automatically checking for software updates and letting users select which ones to install.

IV differs from ordinary patent trolls in several respects. Most patent trolls are paper corporations with empty offices and a skeleton staff. In contrast, IV has a famous founder and a well-staffed Seattle-area headquarters. The firm also built an impressive-looking science lab where IV scientists and engineers develop potentially patentable ideas.

But like all patent trolls, it has been careful not to commercialize any of those inventions. That means that IV is not vulnerable to the threat of retaliatory lawsuits that has helped keep litigation among large technology firms in check.

And that calls into question the value of Google's acquisition of Motorola for its patents. Motorola's patents will serve as a strong defensive weapon against companies like Microsoft and Apple that make products of their own, but defensive patenting is helpless against firms that have no products. Myhrvold was one of the first to recognize this vulnerability, and it appears to be making him a very wealthy man.