Can computer software be patented?
Computer hardware - the physical components of computers - and software - the bits of binary code used to make the computer do what it does so well - are created by inventive individuals, whose design (whether circuitry or for methods for solving problems) can become the object of a patent. Patents are meant to cover ideas, and "anything new under the sun made by man" has long been the subject of patent law; only laws of nature, natural phenomena, mathematics, or other universal truths have not been patentable.
With the approaching merger between biology and computer science, sometimes referred to as DNA computing, offering to revolutionize agriculture and health sciences, even plants, animals, and genes can be patented. Which means that the United States Patent and Trademark Office (or its like in another national government) has granted the creator a property right to the manufacture and use of his or her new design or method, for a term of 20 years from the date the patent was applied for. Nobody else in the country can use that new design or method without license from the patent-holder, until the patent expires. In exchange, however, the patent-holder provides a detailed description of the invention and the best technique he knows of at the time he applies for realizing it. This description is made public when the patent issues, increasing our societal knowledge; and that means that everybody can start working on the next improvement right away. Patents can co-exist with copyrights and trademarks, but not with trade secrets (at least, not for that invention).