There have been multiple leaks of Windows source code. At least one of them included almost everything required to build Windows XP: https://www.zdnet.com/arti

There have been multiple leaks of Windows source code. At least one of them included almost everything required to build Windows XP: https://www.zdnet.com/article/windows-xp-leak-confirmed-after-user-compiles-the-leaked-code-into-a-working-os/ https://www.zdnet.com/article/windows-xp-leak-confirmed-afte... The only missing component was winlogin.exe, probably because of its involvement with the activation process.