How is a computer software patent different from a software copyright?
Any computer program is automatically covered by a copyright, which protects the program from being copied. However, a copyright does not protect the owner if someone were to create new computer code to ultimately do the same thing. For example, suppose I create a computer program that can help me predict the economic movement of the housing market. While my copyright in that program protects me from having you simply copy my program, nothing prevents you from independently creating your own computer program which can also predict the economics of the housing market.
Software patents, however, protect the programming method which underlies the software. Thus, using the above example, if your computer program uses the same methodology to predict the housing market economy as my software, I can stop you from using or selling that program because of my patent, even though you may not have violated my copyright. There is an important distinction here - while a copyright is not violated if the “copier” independently develops the program in question, patent law does not care about how the program was created. So even if you had never heard of or seen my housing market software, your independently created software could still violate my patent. In other words, your knowledge of my rights is simply irrelevant and you have infringed my patent.