Reverse-engineering is not illegal. The Library of Congress ruling specifically grants an exemption from the Digital Millennium Copyright Act for people to modify their software as necessary to continue using it after official support has ended. No, I believe you understand it wrong. It's only allowed to circumvent the DRM (including online DRM) AND it's for museums and such. Preservation does not imply individual play, from what I can get. Also what Lenard was saying (and it was quite painful to watch tbh, because clearly both of you have not enough technical expertise on the topic, so your questions and his responses were all over the place and never actually covered the actual problem core) - basically if the only thing you are making is the server code and just it - then maybe it's legal (though I am still not convinced you are free to reverse the client to do so), but if you are also producing anything else (any asset) - that is covered by copyright and you can't do that. That's what I get from there - i.e. if you have say a Quake style server that basically just relays the messages everywhere and does some simple movement/shooting logic - it's fine. But if it's say Destiny server that have quest definitions only on the server (while all the dialogs, cutscenes, etc are on the client) - if you reproduce them, you actually infringing their copyright on those quests - even if you've never seen the actual server data (and if you not copy them you probably making derivative work, which is also forbidden by the license). No, it's you who've read it wrong, and Ross is correct: The Library of Congress authorizes the bypassing of DRM protections and the backing up and modification of video games for the sake of continued use of the software programs by the people who have bought it. https://s3.amazonaws.com/public-inspection.federalregister.gov/2018-23241.pdf Here's the proposal: And here's the ruling: The part you're talking about, being archived by a museum or similar, is (B), whereas the part Ross mentioned, being able to bypass DRM or modify the software to keep playing it, is part (A). The allowance is for people to modify their software in any way necessary in order for them to continue accessing it in the way it was designed to be used when it was bought. That means that not only may people in the US back up their software and bypass any of its DRM, but they may also do what else is necessary with it in order to continue to use their purchased software. As Ross said, though, copyrighted material cannot be used in the modification. As the Library of Congress ruling says: Outside of the Library of Congress ruling, the Digital Millennium Copyright Act allows people to reverse-engineer software under limited situations. https://www.govinfo.gov/content/pkg/PLAW-105publ304/pdf/PLAW-105publ304.pdf "a person may develop and employ technological means to circumvent a technological measure, or to circumvent protection afforded by a technological measure... for the purpose of enabling interoperability of an independently created computer program with other programs" - this sounds to me as though it already on its own and without the Library of Congress ruling protects reverse-engineering for the purpose of getting a game to interoperate with an OS, in other words, to run properly.