Open source licences

Despite the growth in the commercial importance of open-source software, uncertainty remains as to the legal framework governing its use. This contribution provides an initial overview of the terms to be found in open-source licences.

Open source licences

For years, the importance of open source software has been growing. According to estimates, a third of all software in Europe is open source software.

Many companies use open source software either as full applications or as components within their own commercial software products. Examples of open source software include: the web browser Firefox; Open Office; the operating system used for many servers and smartphones, Linux; the webserver Apache; and database management systems such as MySQL.

Despite the fact that open source software is establishing itself on the mass market, many companies utilise open source software products without paying sufficient or even any attention to the legal framework governing its use. This is the case even though the commercial consequences of illegally using open source software could be severe. This text therefore summarises the legal position in relation to various types of open source software.

1. Definition of open source software

Although there is no recognised general definition, open source software can be characterised as free software which complies with a licence containing the criteria established by the Open Source Initiative.

It is characteristic of such software, that the source code is made freely available and can be reproduced and modified both in its original and modified form.

Nevertheless, it should not be assumed that there are no rules attached to the use and exploitation of open source software. Unlike public domain software, the use of open source software is often permitted only if the user complies with certain conditions.

The condition that all types of open source licences have in common is the requirement for reference to be made to the copyright holder and for the text of the licence to be available with the software.

2. Types of open source licences

Other conditions and obligations contained in open source licences vary depending on the licence. There are three main categories of open source licence.

a) Strong copyleft licences (e.g. GNU General Public Licence)

The so-called strong copyleft licence contains the strictest requirements. The GNU General Public Licence (GPL) is an example of such a strong copyleft licence. Under a GNU GPL, users are required to place any reproduced original or modified software (derivative work) under a GNU GPL licence. This is called the “copyleft effect” and it ensures that the original software and all of its derivatives remain open source.

b) Non-copyleft licences (BSD licence, Apache Licence)

The opposite of strong copyleft licences are non-copyleft licences such as BSD licences (Berkeley Software Distribution). Here, the user is not strictly required to place derivative software under an open source licence and may distribute it under other form of licence.

Non-copyleft licences allow for the development of commercially marketable software products based on open source codes. If the user chooses to market the derivative work under a proprietary licence, the developer would not be required to disclose the software code.

c) Limited copyleft licences (e.g. Mozilla Public Licence)

In between strict copyleft and non-copyleft licences are a range of hybrid forms of copyleft licences which generally permit the distribution of derivative works from open source software under an open source licence. However, in certain circumstances derivative works can exceptionally be made subject to a proprietary licence.

For example, the so-called GNU Lesser General Public Licence (LGPL) enables developers to integrate LGPL software into their own (proprietary) software, without having to release the source code of their own software. The open source parts of the derivative (propriety) software developed under this licence are kept separate and remain under open source licence.

The Mozilla Public Licence (MPL) enables software developers to derive software from MPL source code. The derivative work can be placed under open source or propriety licence. The source code must remain under MPL licence.

The Artistic Licence gives users a choice of several defined licence conditions when distributing software.

3. Problems with using open source software

The distribution of open source software or its use as a basis for developing derivative works can lead to problems such as the the so-called “viral effect”.

Here, a company that uses open source components to help develop commercial software products may find that the newly developed software is subject to the copyleft effect mentioned above.

This could lead to the derivative software and its code, which may have been developed following the expenditure of much time, effort and money, having to be made available under an open-source licence. Consequently, the developed software may become commercially unusable.


Do you have questions about IT law, licences or data protection? We are happy to help!
German lawyer, Christian Solmecke, and his expert team are available to answer your questions.
Call us on +49 (0) 221 / 951 563 0 or use our contact form.


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Christian Solmecke is a partner at the law firm WILDE BEUGER SOLMECKE. He is the author of numerous legal publications in the area of internet and IT law. He is also an associate lecturer for social media law at the Cologne University of Applied Sciences.

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