a. History of software copyright statute
17 USCS § 101 defines a computer program as "a set of statements or instructions to be used directly or indirectly in a computer in order to bring about a certain result."  Section 102(a) defines the subject matter of a copyright as "original works of authorship fixed in any tangible medium of expression, now known or later developed, from which they can be perceived, reproduced, or otherwise communicated, either directly or with the aid of a machine or device."
Section 102(b) limits copyright protection, excluding "any idea, procedure, process, system, method of operation, concept, principle, or discovery, regardless of the form in which it is described, explained, illustrated, or embodied in such work."
Copyright protection was required for computer programs because the sales contract bound only parties to the contract. Someone who "found" a computer program was under no obligation to protect against its unauthorized use.
When the first computer programs were registered for copyright in the 1960s, the U.S. Copyright Office determined that 1) the programs met the "original authorship" requirement, 2) they had been published, and 3) they were "in a language intelligible by human beings," which usually necessitated a printout of the program's source code accompanying the copyright application.
Soon software developers routinely included a copyright notice in their programs even if the programs were not formally registered.
The Copyright Act of 1976 amended the definition of literary works in 17 USCS § 101 to include "computer data bases, and computer programs to the extent that they incorporate authorship in the programmer’s expression of original ideas, as distinguished from the ideas themselves." In 1978, the National Commission on New Technological Uses of Copyrighted Works (known as CONTU) recommended in a report to Congress and the President that purchasers of software be allowed to back up the program and to resell it once without requiring the consent of the original seller:
"The sale of a copy of a program by a rightful possessor [later changed to 'owner'] to another must be of all rights in the program, thus creating a new rightful possessor and destroying that status as regards the seller."
This and other CONTU recommendations were adopted by Congress in 1980. Soon software vendors began licensing rather than selling their products, which introduced confusion about the right of licensees to resell the programs.
For works created after January 1, 1978, the general rule is that copyright protection lasts for the life of the author plus 70 years. For works for hire, the copyright applies for 95 years from first publication or 120 years from its creation.
17 USCS § 504 specifies the remedies for copyright infringement: the copyright owner’s actual damages and any additional profits of the infringer; or statutory damages, which "are a sum of not less than $750 or more than $30,000 as the court considers just" for each work infringed. However, in the case of willful infringement, the copyright holder may collect "a sum of not more than $150,000." Similarly, when the infringer was unaware of the copyright and had no reason to believe the use constituted infringement, the court may reduce the damages to "a sum of not less than $200."
b. Assembling the pieces of the software-copyright jigsaw puzzle
 Hollaar, Lee A., Digital Protection of Digital Information, http://digital-law-online.info/lpdi1.0/treatise17.html