The leaker claims he spent two months compiling this collection and posted the torrent on the 4chan forum. A smaller 2.9GB archive containing just the source code of Windows XP and Windows Server 2003 is also circulating on the web. According to the leaker, this code has been passed around privately between hackers for years now.
This is pretty ancient code but it may still have security implications if exploitable code is found that's still in use by Windows 10.
Even though Windows XP and Windows Server 2003 are very old operating systems, complete source code leak of them is a huge security concern. Because even modern OS like Windows 10 will have several source code files that are untouched from Windows XP days. Hackers can go through the old source code and find bugs to exploit them on Windows 10.