That is not correct and most likely comes from scary FUDs of yesteryear between GPL and anti-GPL crowds (e.g. Microsoft who used to disallow people look at GPL'

That is not correct and most likely comes from scary FUDs of yesteryear between GPL and anti-GPL crowds (e.g. Microsoft who used to disallow people look at GPL'd code). In reality looking at this (or any other leaked on unlicensed code) "taints" you pretty much the same as looking at any other code, including -e.g.- GPL/MPL/Apache2, etc code, but you don't see anyone[0] nowadays saying to not look at such code (it used to be a thing back when people were cluelessly afraid of GPL though, but that was decades ago). The "taint" isn't inherent, it comes from the possibility that you'd rewrite code you've seen so that it is mostly identical and be sued for it (and if that is the case is something that will only be decided by a court). If anything, IIRC when GNU was making their Unix replacement utilities back in the day they recommended people to implement them in as different from Unix a way as they could, but they didn't forbid people who were "tainted" by Unix to contribute to GNU (which, if you think about it, makes perfect sense considering the people who would contribute to it were most likely already Unix programmers). This sort of remains in the current GNU Coding Standards[1] In fact you are "tainted" the same way by read and/or participating in any codebase that isn't fully owned by yourself - but if that was an actual problem in practice, no programmer would be able to join another company unless what they did there had absolutely nothing to do with any of the companies they worked at previously as experienced programmers would actually be liabilities[2]. Meanwhile in reality programmers jump between companies all the time with their experience being seen as an asset. [0] don't take that literally, i'm certain some people would recommend against reading GPL/MPL/etc code, but they'd be a very tiny minority - and almost certainly driven by the same old FUDs [1] https://www.gnu.org/prep/standards/standards.html#Reading-Non_002dFree-Code https://www.gnu.org/prep/standards/standards.html#Reading-No... [2] Yes, you can find anecdotes where that happened - John Carmack being sued by ZeniMax would be such a case - but those are very rare exceptions from litigious sue-happy companies and there are literally millions of professional programmers out there