In its decision, the BPAI announced a new two-pronged test for determining whether an invention involving a mathematical algorithm would be eligible for patent protection. First, the invention must be "limited to a tangible practical application" and result "in a real-world use." Second, it must be "limited so as to not encompass substantially all practical applications of the mathematical algorithm" in all fields or even in "only one field.
via arstechnica.com