The U.S. Copyright Act does not contain provisions explicitly dealing with "reverse engineering" or decompilation of computer programs. Under U.S. law, copying or reproducing computer programs without the permission of the program owner is not permitted unless excused by the provisions of the "fair use" doctrine or as back-up copying under section 117.

The fair use provisions embodied in the U.S. statue attempt to balance user and proprietor interests through the application of four factors set forth in the statute which are discussed in detail later in this paper. On their face these four factors appear to be imprecise. However, operation of the statute, including the four fair use provisions, has provided a workable framework for courts to decide cases and for parties to determine what is appropriate behaviour.

U.S. Copyright Act


The U.S. Copyright Act was thoroughly revised in 1976. Although no definition of computer program was contained in that Act, the legislative history makes clear that Congress considered computer programs were already subject to protection as literary works. The 1976 Act did not contain any special limitations on computer programs, an issue that the National Commission On New Technological Uses Of Copyrighted Works (CONTU) was studying. In 1978, CONTU issued its report, and in 1980, Congress adopted CONTU's recommendations, as modified. The exclusive rights enjoyed by authors of computer programs under the Act are exactly the same rights specified for all other non-dramatic literary works, with the exception of a personal use exemption for the making of a back-up copy and adaptation as necessary for use of the program.

In analyzing how decompilation would be treated under U.S. copyright law, it is important to keep in mind the basic structure of the 1976 Copyright Act. That structures enumerates categories of protectable works of authorship [s.102(a)] and gives them broad, exclusive rights [s.106]. The breadth of drafting is intended to permit innovative forms of authorship and marketing to be absorbed into the existing copyright system without the need for frequent legislation to deal separately with each new technological change. By contrast, limitation upon and exemptions from exclusive rights are drafted with great specificity, and are restricted to certain works, uses, user groups and purposes [s.107]. Many areas are deliberately left to the courts to elaborate in the context of specific disputes. For example, the Copyright Act does not define "author", "originality", or "infringement". Neither does it define "idea" nor "expression". In the area of limitations on exclusive rights, the statute codifies the judge-made doctrine of fair use and lists several factors to be considered in evaluating fair use claims, but leaves it up to the courts how to weigh and apply those factors in each case.

Rights Granted

The following sections of the U.S. Copyright Act are relevant to the issue of decompilation: s.101, which contains a definition of computer programs; s.102(a), which extends protection to literary works (a category that includes computer programs); s.102(b) which declares as unprotectable ideas, methods of operation, processes, procedures, systems, concepts, principals and discoveries; s.106(1) and (2), which grant copyright owners of computer programs the right to reproduce their works and to create derivative works, s.107, which codifies the fair use doctrine; and s.117, which creates a limited personal use single back-up copy and adaptation exemption for computer programs.

These provisions do not grant a generalized right to make unauthorized copies of substantial parts of computer program expression. The U.S. statue and decided cases do not prohibit study and research uses of any work, including computer programs. Such use can include incidental, insubstantial or inconsequential copying. Such activities, however, are subject to the general limitations applicable to all protected works.

Under U.S. law, unauthorized reproduction or translation of substantial parts of a program's object code into source code would result in a prima facie violation of the copyright owner's rights to reproduce the work and to make derivative works, granted in s.106(1) and (2). As a technical matter, this is the case regardless of whether the activity is undertaken independently or as part of a decompilation process.


A party accused of violating the protection granted by the copyright law could raise a number of potential defenses. These include denial of copying and proof of original creation of the allegedly infringing program, attacking the copyrightability of the allegedly infringed program; arguing that copying was limited to unprotected elements of the program (e.g. ideas, or expression inextricably merged with such ideas); or, that the copyright was exempt under a specific provision of the copyright act. Whether any of these possible defenses will apply to prima facie unauthorized reproduction, including decompilation, depends on the precise facts of a given case, including who is doing the copying and for what purpose.

Section 117 - Back-Up Copies

Section 117 of the U.S. Copyright Act, as amended in 1980, accords to lawful owners of copies of computer programs the equivalent of a limited personal use exemption. Under that section, a single back-up copy may be made to protect against inadvertent destruction of the copy, while adaptations may be made "as an essential step in the utilization of the computer program in conjunction with a machine and that it is used in no other manner."

As a strictly personal use exemption, the section provides that all archival copies must be destroyed in the event of continued possession of the computer program. The ability of those who lawfully possess copies by lease or license arrangements to adapt or make single back-up copies is determined solely by contract.

Section 117 serves two purposes: first, it permits an owner of a lawful copy to protect himself/herself against mechanical destruction of their copy by permitting him/her to make a single back-up copy; second, it permits such an owner to adapt the program as necessary to run it on his/her individual machine. At the same time, it protects copyright owners by prohibiting transfer of copies made under the exemption without permission. Since s.117 provides only a limited personal use exemption, it is unlikely to excuse the reproduction of a computer program for research and development purposes.

Section 107 - Fair Use

The only other statutory defense to unauthorized reproduction is fair use, a judge made doctrine, now codified in s.107. Section 107 is at annexure A to this paper.

The following paragraphs outline the step by step analysis a court must undertake in applying a fair use defense in a decompilation case. The structure of s.107 is twofold. First, a number of activities are set out as specific examples of the kinds of uses which may typically involve fair uses: criticism, comment, news reporting, teaching, scholarship or research. Of relevance to decompilation is the section’s reference to "research". We will assume here that decompilation may be regarded as "research", an assumption that is open to question.

The section then directs an examination of four, non-exhaustive factors:

  1. the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;

  2. the nature of the copyrighted work;

  3. the amount and substantially of the portion used in relation to the copyrighted work as a whole; and

  4. the effect of the use upon the market for or value of the copyrighted work.

Purpose and Character of Use

Some have argued that when the purpose of decompilation is to gain access to the "idea" of the computer program, fair use ought broadly to be applicable to such activities. Section 102(b) of the Copyright Act, however, denies protection to ideas. The lack of protection for ideas does not limit the copyright owner’s rights to protect the original expression of such ideas, and fair use is an affirmative defense to the taking of expression.

A U.S. court, in a decompilation case, would examine two preliminary questions: (1) what are the "ideas" expressed in the particular program; and (2) is there a need to decompile the program in order to gain access to those ideas.

The separation of an unprotectable idea from its protectable expression has often been a difficult task in copyright litigation. The tendency of U.S. courts in computer cases has been to define the idea elements of a computer program quite generally. This can have the effect of conferring upon the great bulk of programming – text, structure, sequence or organization – the idea of a business management program as "the efficient operation of a dental laboratory". Decompilation would certainly be unnecessary to gain access to an idea at that level of generality. Other courts may take a more detailed approach to the issue in particular cases, and define the idea in a more specific and technical way. Decompilation may be required (but not necessarily justified) to gain access to that idea. Additionally, a court could consider relevant whether the embodiment of the idea in complex coding makes access to that idea impossible (or materially more difficult) without reproduction of the expression.

As a second step a court would consider whether there are alternative methods of understanding the idea, such as by examining published literature and manuals, or, by running special test programs designed to reveal how the program works.

The underlying purpose of the decompilation would be very relevant; is it being genuinely done to learn concepts, or is it being done as a short-cut to unfairly avoid doing one’s own research in order to come up with an original program; to do indirectly what the copyright law does not permit to be done directly? In construing the first fair use factor, in one case the U.S. Supreme Court observed that every commercial use of copyrighted materials is presumptively an unfair exploitation of the monopoly privilege that belongs to the owner of the copyright. This holding is based on the distinction in the statute between nonprofit educational and commercial uses – for example, decompilation by a computer science professor for teaching purposes, and decompilation by a for-profit corporation with a commercial purpose. Yet, even there, much remains to be examined by the courts. As a practical matter, the vast bulk of litigation in the U.S. involving successful and futile claims of fair use has been between competing commercial entities. The legislative history of the 1976 Act affirms that the privilege of fair use is potentially applicable to all categories of users, notwithstanding the apparently preferred status accorded non-commercial educational and scholarly uses.

Nature of Copyright Work

The second factor is the nature of the copyrighted work. With computer programs, object and source code versions of the same program may receive quite different treatment for purposes of applying "fair use" to unauthorized activities. Current industry practice in many cases is to distribute commercially only object code versions of a computer program, whereas source code is not distributed (hence published, within the technical meaning of U.S. Copyright law). The availability and scope of fair use has tended to be narrower in the case of unpublished than of published materials. The fact that the nature of the work was published object code would weigh in the decompiler’s favor, while, the fact that the nature of the work was unpublished source code could weigh against the decompiler. Determination of this factor is clouded by a decompiler’s ability to take published object code and gain access to at least an analog of the unpublished source code.


The third factor is the amount and substantiality of the portion used in relation to the copyrighted work as a whole. This has involved both quantitative and qualitative analyses. In general, however, outside of home taping of free broadcast television programming, instructional activity in classrooms and certain library activities, the copying of entire works is not permitted. To the extent that decompilation typically involves reproduction of substantial parts, if not the whole, of the work, this factor could be weighed against the decompiler.

Market Effect

The final factor is the potential market effect of the unauthorized use: the copyright owner need not show actual harm. The Supreme Court has held that every commercial use presumptively results in harm to the market, and thus, commercial decompilers will have to overcome that presumption.

Arguments have been made, though, that this factor only concerns harm from the taking of expression. If the decompilation does not result in an end product which is substantially similar in its overall expression, acceptance of this argument would result in the fourth factor being weighed in the decompiler’s favor. U.S. courts, however, may not take such a technical view of the issue, and may instead focus on head-to-head competition and market displacement.

Annexure A

Section 107. Limitations on exclusive rights; Fair use

Notwithstanding the provisions of sections 106 and 106A, the fair use of a copyrighted work, including such use by reproduction in copies or phonorecords or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research is not an infringement of copyright. In determining whether the use made of a work in any particular case is a fair use the factors to be considered shall include –

  1. the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;

  2. the nature of the copyright work;

  3. the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and

  4. the effect of the use upon the potential market for or value of the copyrighted work.

The fact that a work is unpublished shall not itself bar a finding of fair use if such finding is made upon consideration of all the above factors.

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