Decompilation, defences and copyright: CJEU Top System Decision


In a decision dated 6 October 2021, the Court of Justice of the European Union (CJEU) has clarified that a lawful user of a computer program may decompile that program in order to correct errors that affect its operation. However, the Court also confirmed that the user may only decompile the program to the extent necessary to correct the error and in compliance (if relevant) with any conditions set out in the end user licence agreement.

The facts

Top System SA, a Belgian company, had developed various software applications for SELOR, a Belgian governmental agency. In particular, Top System had developed framework software (Top System Framework, or “TSF”), which it licensed subsequently to SELOR. In 2008, the parties exchanged communications concerning technical errors affecting certain applications using TSF. Top System failed to reach an agreement with SELOR to resolve those issues and consequently brought proceedings against SELOR, claiming that it had decompiled the TSF, thereby breaching Top System’s copyright in the software.

By way of background, a computer program is initially written in the form of source code, in a particular programming language. It is then transcribed into object code - which the computer can understand/interpret - using a process known as compilation. By contrast, decompilation is a process that is intended to translate a computer program’s object code into source code. However, typically the source code that is reconstructed through decompilation comprises a ‘quasi’ version of the original. In turn, that quasi source code can be amended and compiled into object code, thereby enabling the program to function.

SELOR acknowledged that it had decompiled the TSF software, although only for the purposes of rectifying the technical error by disabling the defective function.

The Belgian first instance court dismissed Top System’s case. Top System then appealed that decision to the Brussels Court of appeal, which referred the following questions to the CJEU:

  1. Is Article 5(1) of Directive 91/250 to be interpreted as permitting the lawful purchaser of a computer program to decompile all or part of that program where such decompilation is necessary to enable that person to correct errors affecting the operation of the program, including where the correction consists in disabling a function that is affecting the proper operation of the application of which the program forms a part?
  2. In the event that the question is answered in the affirmative, must the conditions referred to in Article 6 of the Directive, or any other conditions, also be satisfied?

The relevant law

Article 4 of Directive 91/250 (the “Directive”) specifies the exclusive rights bestowed to the proprietor of copyright in a computer program, which include the right to prevent the: permanent or temporary reproduction of a computer program, in part or in whole; and ‘translation, adaptation, arrangement and any other alteration of a computer program and the reproduction of the results thereof’. However, Article 5 of the same Directive stipulates certain circumstances in which – in the absence of contractual provisions to the contrary – those acts will not require the authorisation of the rightsholder, including:

  • Where they are necessary for the use of the computer program by the lawful acquirer in accordance with its intended purpose, including for error correction;
  • Where the lawful acquirer of the computer program, while loading, displaying, running, transmitting or storing the program, observes, tests or studies the function of the program to identify the underlying ideas and principles of the software.

Article 6 of the Directive also outlines the specific circumstances in which a computer program can be decompiled lawfully, namely where the reproduction and translation of the code are necessary to achieve the interoperability of an independently created computer program.

Decision of the Court

In considering the first question referred, the CJEU noted that neither Articles 4 nor 5 of the Directive mention the act of decompilation specifically. The Court therefore set about determining whether Article 4 of the Directive (to which Article 5 refers) could be construed to include the act of decompilation. The Court considered the process of decompilation as set out above and concluded that it constitutes an alteration of the program code, which involves (a) a reproduction of that code (at least in partial/temporary form) and (b) the translation of the form of that code. The Court noted consequently that the acts of reproduction and translation are reserved exclusively for the owner of the copyright in a computer program under Article 4 of the Directive. Accordingly, the Court held that decompilation does indeed fall within the exclusive rights afforded to the author/owner of copyright in a computer program.

Turning to the exceptions under the Directive, the Court noted that pursuant to Article 5 a lawful acquirer of a computer program is already entitled to reproduce and translate the underlying code without seeking permission from the rightsholder, provided that such acts are necessary for the use of the program, including for the correction of errors that impact on the functionality of the program. As such, Article 5(1) of the Directive should therefore also be interpreted as authorising a lawful acquirer to decompile a program to correct errors that affect its functionality.

Top System had argued that the Directive only permitted decompilation in circumstances where it was necessary to ensure interoperability with another independently-created computer program (mirroring the wording of Article 6). However, the Court dismissed Top System’s interpretation, holding that the respective purposes underlying Articles 5 (lawful exception for reproduction/translation) and 6 were different. Indeed, applying Top System’s interpretation, the ability of a lawful acquirer to correct errors in a computer program would be restricted severely, which would undermine the application of Article 5 altogether.

In conclusion, then, the Court held that Article 5(1) of the Directive should be construed as meaning that a lawful purchaser of a computer program is entitled to decompile all or part of that program in order to correct errors affecting its operation, including where the correction consists of disabling a function that is limiting the proper application of the program.

Turning to the second question referred, the Court noted that the exception provided by Article 6 of the Directive was different in both scope and purpose to that laid down in Article 5. Nonetheless, the CJEU specified that the lawful decompilation of a computer program was subject to the following conditions:

  • The act must be necessary for the use of the computer program by the lawful purchaser in accordance with its intended purpose, including for ‘error’ correction. In the absence of a statutory definition, the Court noted that an error “commonly designates a defect affecting a computer program which is the cause of the malfunctioning of that program”;
  • The act of decompilation must be necessary for the lawful purchaser to be able to use that program in accordance with its intended purpose;
  • Decompilation – which involves obtaining access to the program’s source code or quasi-source code – cannot be regarded as necessary where the source code is already lawfully or contractually accessible to the purchaser;
  • The exception under Article 5(1) that allows errors to be corrected is subject to ‘specific contractual provisions’, although the recitals to the Directive make clear that the correction of errors affecting the operation of a program cannot be prohibited by contract. Balancing the apparently contradictory wording, the Court concluded that while the parties cannot prohibit the correction of errors by contractual means, they are free nonetheless to agree that the rightsholder will maintain the program in question, including by carrying out corrections thereto;
  • The lawful purchaser of a computer program who has decompiled that program in order to correct errors is precluded from using the results of the decompilation for purposes other than the correction of errors.

Key take-aways

The CJEU’s decision reinforces the circumstances in which a lawful purchaser/acquirer of a computer program is entitled to copy, translate and, ultimately, decompile that program without fear of liability for copyright infringement. The decision is useful insofar as it clarifies that decompilation is captured specifically by the existing permitted acts of reproduction and translation, which should provide some reassurance to licensees of computer programs in the event that they attempt to rectify errors themselves. Of course, licencees/lawful acquirers should bear in mind that decompilation will not be permitted where the source code has already been made available. In determining that rightsholders are permitted to regulate by contract the ‘corrective maintenance’ of a program, the Court appears, however, to have limited the circumstances in which a lawful acquirer can take steps themselves to carry out remedial action. Where, for instance, a software company agrees under the terms of its licence to issue ‘patches’ to update a program in response to a particular error, that would appear to limit the lawful user’s legal ability (as well as its practical incentive) to make those amendments itself.