I have created a piece of software that converts a proprietary format from the database blob of a large, well known commercial software company into the equivalent open source data type. The large commercial software company states the following on their copyright and trademarks page "This work is protected under United States copyright law and other international copyright treaties and conventions." and links to the DMCA.

I was able to create the software because most details of the format were published in a post on their support forums and the rest I reverse-engineered.

I now wish to open-source my software so others can use it. My question has two parts:

  1. Can I open-source this at all without getting sued?
  2. Can I refer to the trademarked product the file format came from in my software and documentation? (I'm assuming I can't use it in the name of my software)

I'm in the UK. The large software company is in the US.

  • Did you copy any of their work?
    – user3851
    Apr 4, 2016 at 15:27
  • This question might do better on Open Source.
    – feetwet
    Apr 4, 2016 at 15:36
  • Do the terms of use of the support forum include any language which says that, by using it, you agree not to use the information there to reverse engineer any of their products? There is a number of questions similar to that one which need to be asked. And depending on which of the answers (if any) happen to be "yes", it may be a violation of some of the agreements, that you have made, to publish such software. You may be better off changing the question to ask what are such questions whose answers may control the legality of publishing such software.
    – grovkin
    Jun 1, 2021 at 14:32

2 Answers 2


The words "proprietary format" are important.

Are you sure the format is proprietary? If it is, then it's likely protected in which case they might have grounds to sue (but that does not mean they would definetly win).

If the format is not proprietary, and so long as you don't share data which is proprietary then I believe you fine.

I'm not a lawyer - but I cite GIF files as an example. They were still protected by the US and some other countries until at least the late 90s and there were various threats to open source linux companies who shared code that used the file format. I'm not aware of anything other than threats and never heard of any company being sued, let alone winning or losing.

Another example that comes to mind is the RedHat ISO format. My understanding is RedHat could not stop anyone from sharing open source, but they could prevent folks from sharing the format they assembled and shared the open source. Again, I am not sure if it was ever tested in any court of law anywhere.

  • 1
    "RedHat ISO"? I'm not aware of any new format they have invented; the ISO 9660 file format on its own is certainly not Red Hat's, it's only the contents which are.
    – user1686
    Jul 7, 2016 at 10:41
  • 1
    I can see how you misunderstood what I wrote... Let me clarify... The physical data - the ones and zeros so to speak - if you were to physically duplicate a Red Hat installation DVD, you would be breaking copyright law. They realised they could not protect the software, but they could protect the effort they put into assembling the software as it is a source of income for them.
    – fiprojects
    Jul 8, 2016 at 10:40
  • 1
    I suspect what the OP wants to do will ruffle feathers but could be considered legal. I see it akin to using Torrent. Have a Torrent program on your computer is not illegal, but using it to download a movie would be illegal - thus, I see this akin to the OP having written something like Torrent (a tool that shares data) and that the act of breaking the law would depend on a user using the tool to copy data that is protected.
    – fiprojects
    Jul 8, 2016 at 10:46
  • 1
    @fiprojects are you saying that using a tool to transform let's say a docx into a different format, e.g. a png is breaking the law? So even making screenshots could be considered to be illegal?
    – lucidbrot
    May 6, 2018 at 10:20

There's several different parts to this.

  1. Is it legal to reverse engineer the program
  2. Is it legal to reverse engineer the format (from files)
  3. Is it legal to distribute software that consumes the proprietary format
  4. Can you be sued for any of this

For #1, EFF has a good FAQ for the US.

Acts in the UK up to 2020 (Brexit) would be covered under EU Directive 2009/24/EC, which makes reverse engineering for compatibility purposes legal in many circumstances (including if you don't have the author's permission to use the software). This article has a good overview.

For #2 it's important to know that the output of a program is not copyrighted by the author of a program, although it might be copyrighted by the user who operated the program.

So you should have permission to hold a copy of the files you're inspecting if they contain copyrightable elements (for example, the text inside a .doc file belongs to the person that wrote it).

#3 could be illegal if there's a software patent.

Famously the distribution of software that read GIF files was hampered by a patent on the LZW compression method. Another famous example is Microsoft's FAT filesystem, which resulted in lawsuits to companies reading SD cards.

In some of these cases people found restricted ways of reading the formats that were not covered by the patents.

This is extremely dependent on your jurisdiction. You might want to consider publishing your program from a friendly jurisdiction to avoid legal problems

#4 is the easiest to answer. You can be sued by anyone for any reason at any time.

Lawsuits involving proprietary formats are usually brought against commercial use of the format (as in the FAT case).

If you're working on open source and a company threatens to sue you and you're confident what you're doing is legal you might want to consider asking for legal assistance from the EFF

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