Many software license agreements (or even terms of sale for physical copies) include prohibitions on reverse engineering as a condition. If I legitimately purchase and install and use the software, I have then contracted to not reverse engineer the software. If I turn around and do it anyway, and, say, develop a competing product that eats into sales of the original, my understanding is that I could be sued for damages for those lost sales because of my breach of the contract.

Does the same principle apply if I do not get an available license and instead deliberately infringe copyright?

If I reverse engineer the software by downloading a copy off The Pirate Bay instead of by buying a licensed copy, I would be liable for damages for having made a copy without permission. But say I take that copy and turn around and reverse engineer it, without making any more copies, and I launch a competing product that does not itself constitute a derivative work. Would I be liable for damages for lost sales on the original software resulting from reverse engineering that I was only not prohibited from doing because I infringed copyright? Or would I only be liable for statutory or actual damages for my infringing copies of the original software?

  • Reverse engineering a piece of software from a copy... I am a bit confused here... Are you reverse engineering the interface (legal) or coping the program. Reverse engineering a modern piece of complicated software is harder then just building the thing from scratch.
    – Questor
    Commented Feb 16 at 20:27
  • 2
    @Questor these follow-up questions of your seem irrelevant to the original question. Commented Feb 16 at 20:46
  • What he is trying to reverse engineer matters. THere are certain types of reverse engineering that are always legal in the united states.
    – Questor
    Commented Feb 16 at 20:50
  • If his 'reverse engineering' is breaking a bit of software into chunks rearranging how things are connected and then sewing it back together like Frankenstein's monster... That is different from interacting with the software and say duplicating functionality that you obvserve and/or copying the interfaces that are exposed to plug-ins/backends/etc...
    – Questor
    Commented Feb 16 at 20:56
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    @Questor I'm imagining that this software has some singular ability or "weird trick" that I want to duplicate in my own software, but I need to know how it was done to replicate it. Maybe it has inside it a table of all the commands for a piece of hardware and what they mean, not available elsewhere, and I also want to write control software for that hardware. Or maybe it is able to compute some value according to a special procedure and I also want to write software to compute that value because there is a market for it.
    – interfect
    Commented Feb 17 at 13:49

1 Answer 1


I would strongly recommend against piracy... It's illegal.

That being said in regard to ToS.. there are certain types of reverse engineering that ToS cannot legally prevent you from doing. Any claims that they can are ilegal, and unenforcible... Sadly I don't know of any companies that have been fined for claiming all reverse engineering is illegal.

That being said Reverse engineering is only 'always legal' if it is done for a small set of reasons.

  1. Software interoperability (IE writing a program that can unzip a file, talk to some hardware, use a backend etc...)

  2. Cybersecurity (Reverse engineering for vulnerability testing is always legal).

  3. there might be some other edge cases.. Consult with an IP lawyer.

When building a product that involves reverse engineering someone else's product. Keep in mind:

  1. it is not legal to copy functionality that is patent protected.

    • That being said, Mathematical formulas and other similarly abstract ideas cannot be legally patented. And a ToS that prevents you from duplicating said behavior might not stand up in court (Don't know for sure, its never been brought up in court that I know of). Except of course for abstract methodologies related to cryptographic operations which for some reason are patentable... Don't ask me why.
  2. Its important to make certain that you cannot be accused of copyright violations etc... And the only method of reverse engineering a software/electronic product that has stood up in court is clean room reverse engineering.

  • one room where the guys who reverse engineer the software work. And another room where the guys that build your software work. And the only communication you allow between those groups is a an SRS that describes the interface... Not how it was implemented.. But what it needs to do to communicate. That is how accord was able to reverse engineer SEGA game cartridges and win against SEGA's lawsuit.
  • This answer doesn't seem to be on point. AIUI, the question is about a situation where there is no ToS in force, because you never actually licensed the software before reverse-engineering it.
    – Barmar
    Commented Mar 22 at 20:42
  • @Barmar Downloading a pirated copy of software is illegal. And you can be sued for that. The only legal way that OP can get the software is to purchase a copy and install it. Installing software, always, always forces you to agree to the TOS. (at least all modern software that I know of). If the OPs goal is to avoid a lawsuit.. OP should not use a pirated copy of the software.
    – Questor
    Commented Mar 22 at 21:12
  • The OP said "deliberately infringe copyright", so I think he knows all that. The question is whether TOS restrictions apply to illegally-obtained copies, or only to legitimate purchasers (since the purchase assents to the TOS).
    – Barmar
    Commented Mar 22 at 21:16

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