Yes, the OSD tries to include legality in "seeing and modifying". If you regard Open Source as just "seeing and modifying" the source then anything that you can get the source code for is Open Source. This is most definitely not the case, as illustrated by my previous example of Windows 2000. Please see [0] and [1] for more info. Confusingly, there are still copies of the W2K source on github which have an MIT license in the root which is, I assume, false and unauthorized by MS [2].