If you're asking if they are formally allowed to do it, the answer is definitely no. If though, you're asking if they "can" in very generic terms, yes, certain

If you're asking if they are formally allowed to do it, the answer is definitely no. If though, you're asking if they "can" in very generic terms, yes, certainly - as a matter of fact, this has been a large controversy of ReactOS. There are no certainties, as everybody has their own side of the story. An MS developer, Axel Rietschin, publicly expressed his opinion that there are wholesale ripped off (low-level) functionalities¹; I personally find it convincing, although it's fuzzy, as he doesn't give details. ¹=https://news.ycombinator.com/item?id=20341933 https://news.ycombinator.com/item?id=20341933