The process of comparing two software programs, whether versions of the same program or from two different sources, to look for similar or identical code in each. A computer program, both in source code and in object code can be regarded as a series of alpha-numeric strings. If there are large areas of coincidence between one program’s code and another (i.e., identical strings are found in each) this coincidence is considered strong evidence that some of one program was copied from another, a potential copyright violation.
However, not all coincidences mean that part of a program was copied. Software techniques often use similar algorithms loaded from public libraries, or they may contain utilities intended to interact with the same feature of an operating system of a CPU on which programs are run, resulting in some partial code commonality.