"For a process to be patentable, it must involve a physical transformation to a different state or thing, or must be tied to a particular machine. What does that mean? The court gave examples indicating that software would be patentable if it represented physical objects undergoing physical transformation. However, it expressly reserved judgment on the alternative test: whether a general-purpose computer was "a particular machine." If so, of course, all software processes would be patentable. Not the brightest of lines, but the court didn't flinch from trying to draw one, despite arguments that patent lawyers would manage to circumvent any court-imposed limitations."
Source: http://www.huffingtonpost.com/brian-kahin/npes-and-abstract-patents_b_156350.html


