Two computer programs can be identical and yet there will be no copyright infringement if both were created independently of each other. One common way of doing this is by creating a “clean room.”
Timothy B. McCormack, lawyer in Seattle, writes: One may independently develop a competing program by having a first team produce design documentation of inputs and desired outputs after lawfully analyzing a first program from which the competing program is to be developed. A second team then writes code for the competing program based on the created design documentation. The competing program, even if substantially similar to the first program will not likely infringe any copyrights because of its independent creation.