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Decompilation of a computer program to remove errors

There are no computer programs that run faultlessly. Sooner or later there will be errors that need to be fixed. In many cases this will mean that changes will have to be made to the source code of the software, i.e. the original form of writing a computer program. However, except in the case of dedicated software, i.e. software developed entirely for the ordering party, licensees do not have access to the source codes of the purchased software. They usually possess software expressed in the form of object code, from which the source code can be reconstructed (decompiled) and only then necessary corrections or additions can be made to it, e.g. to remove errors.

A question arises here as to whether a person authorised to use the software (a licensee) may decompile a computer program on his own without the consent, or even knowledge, of the author, or must he seek such consent from the licensor? This issue was recently decided by the Court of Justice of the European Union (“CJEU”). In a judgment dated 6 October 2021. (reference C-13/20), the CJEU allowed the authorised owner to decompile a computer program itself in order to repair the errors of the software, but under certain conditions.


The case decided by the CJEU concerned a dispute between Belgian entities – a software developer and a public administration body that used the software under licence. The software delivered to the contracting authority consisted of elements of the supplier’s framework software and dedicated functions intended to meet the specific needs and requirements of the contracting authority. Due to emerging problems with some elements of the software and the failure of the parties to agree on a solution, the contracting authority decompiled the software in order to fix it. In response, the supplier brought an action against the contracting authority before a Belgian court, seeking in particular a declaration that the contracting authority had decompiled the framework software in breach of the supplier’s exclusive rights as software developer, and an award of damages for the decompilation and reproduction of the source codes of the software, together with interest.

After the claim was dismissed, the case went to the Court of Appeal. The supplier maintained its position, arguing that the contracting authority had unlawfully decompiled the software, pointing out that such an operation could only be performed without the author’s consent in order to ensure interoperability of the software with other software, and was not permitted in order to correct software errors. The contracting authority admitted that, being entitled to do so, it had performed the decompilation in order to correct certain design errors that the programme contained and that prevented its use for the intended purpose.

In those circumstances, the Brussels Court of Appeal suspended the proceedings and referred two questions to the CJEU for a preliminary ruling:

  • Is Article 5(1) of Directive 91/250 to be interpreted as permitting the lawful acquirer of a computer program to decompile all or part of that program in the event that such decompilation is necessary to permit him to rectify errors affecting the functioning of that program, even where the correction consists in disabling a function which interferes with the proper functioning of the application of which that program forms part?
  • If the answer to the first question is in the affirmative, must the conditions laid down in Article 6 of the Directive or any other conditions also be satisfied?

In answering the questions posed for a preliminary ruling, the CJEU held that Article 5(1) of the Directive permits the decompilation, in whole or in part, of a program for the purpose of correcting errors affecting its functioning, and the lawful acquirer is not required to comply with the additional requirements provided for in Article 6 of the Directive.

Practice of license agreements

The licence terms for the supplied software are often unfavourable to the ordering parties, often directly preventing them from undertaking any activities aimed at analysing, disassembling or decompiling the source code, even for the purpose of servicing (maintaining) the software and debugging it. Selected suppliers go a step further, limiting the right to any development, translation, adaptation and other interference with the source code or the resulting code, including for the purpose of ensuring interoperability with computer programs. Let us recall that under the provisions of the Directive and the Polish Act on Copyright and Related Rights, the right to decompile a program is allowed if it is necessary to obtain information necessary to achieve interoperability of an independently created computer program with other computer programs.

What might be the reasons for contractual restrictions on interfering with purchased software, including performing decompilation to fix software bugs? If you don’t know what’s at stake, it’s usually money. Software maintenance is an additional source of income for suppliers, which nobody wants to give up. The ordering party, having its own highly qualified IT staff, would often be able to remove diagnosed software errors on its own, but such actions (decompilation and interference with the source code) could expose it to liability for breach of contract.

In many cases, in the case of large and complex systems, the ordering parties do not decide to maintain the software on their own and negotiate the service contract and SLA conditions while the system is still being implemented. It should be borne in mind, however, that in the case of the aforementioned contractual limitations, the ordering party is, in a way, at the mercy of the supplier and in the event of a failure of the negotiations and failure to conclude a service agreement, or in the event of a potential dispute and termination of cooperation with the supplier, it is left without the right to repair software errors on its own, for which it has often paid a considerable amount of money.

As software suppliers emphasize, the price for implementation and licensing of software is often calculated on the assumption of future profits related to the provision of maintenance services. With such an assumption, it is difficult to convince the supplier to give consent for decompilation and independent removal of software errors by the ordering parties.

Summary and conclusions

The Court has confirmed the right of a lawful user to decompile a computer program himself in order to correct errors affecting its functioning. This means, in particular, that the contractual clauses underlying the use of the software may not exclude any possibility of correcting those errors. Such clauses must be treated as null and void. The Court expressly confirmed this in the grounds of its judgment, pointing out that ‘the parties cannot contractually exclude any possibility of correcting those errors’.

At the same time, the Court points out that the copyright holder and the acquirer are free to contractually determine the rules for the exercise of that right. In particular, they may agree that the copyright holder is obliged to provide maintenance which includes the repair of defects in the program in question. This means that, in the absence of specific contractual provisions, the authorised acquirer of a computer program may, without the prior consent of the copyright holder, carry out a decompilation of the program if this proves necessary in order to correct errors affecting the functioning of the program. Doubts may therefore arise as to whether the contractual provisions relating to the servicing of the software against payment constitute a premise preventing the user from carrying out the decompilation itself in order to rectify the errors? Therefore, when creating contractual obligations for software licences, the discussed CJEU judgment should be taken into account.

However, decompilation performed for the purpose of removing software errors, on the basis of regulations interpreted by the Court, may not be performed in an arbitrary manner and without any limitations. In this regard, the Court indicated certain conditions for the legality of such action. First, decompilation may be carried out only by a lawful user of the software. Secondly, decompilation may be carried out only for the purpose of correcting identified faults in the program, which means that the results of such decompilation may not be used for purposes other than correcting the faults, for example for the purpose of developing the software according to one’s own ideas. Thirdly, the acquirer is entitled to decompile only to the extent necessary to correct the errors, which in turn means that if this purpose can be achieved by decompiling part of the software, the acquirer is not entitled to recover the entire source code of the software.

In conclusion, it should be noted that there is no doubt that both the source code and the object code, as two forms of expression of a program, are covered by copyright protection granted to computer programs. Consequently, the decompilation of a programme and the related reproduction of the code and its translation fall within the exclusive rights of the author and require authorisation from the copyright holder. The CJEU judgment only confirmed that such authorisation is not required when decompilation is necessary to correct errors in legally acquired software.



Maciej Dudek, specialises in intellectual property law, in particular copyright law, advertising law, as well as unfair competition, consumer rights, protection of personal rights and e-commerce.

#CJEU #contract #copyright law #ECJ #judgment #software

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