IBM is threatening to pursue legal action against TurboHercules, a company that sells services relating to the open source Hercules project, an emulator that allows conventional computers with mainstream operating systems to run software that is designed for IBM System Z mainframe hardware. In a letter that IBM mainframe CTO Mark Anzani recently sent to TurboHercules, Big Blue says that it has "substantial concerns" that the Hercules project infringes on its patents. The letter is a brusque half-page, but was sent with nine additional pages that list a "non-exhaustive" selection of patents that IBM believes are infringed by the open source emulator.