Microsoft’s original Xbox console source code has leaked online, alongside code for a version of Windows NT 3.5. The Xbox source code includes the kernel for the operating system on the original console, a custom version of Windows 2000. We can confirm the leaked Xbox OS is genuine, and appeared online earlier this month. “We’re aware of these reports and are investigating,” a Microsoft spokesperson said in a statement to The Verge.

While the Xbox OS leak includes some build environments, the Xbox Development Kit, emulators used for testing, and internal documents, we understand this kernel and source code has been passed around privately among enthusiasts previously. That means it’s unlikely to help further homebrew and emulator efforts for original Xbox games.

A number of emulators exist for the Xbox, including CXBX, XQEMU, and CXBX Reloaded, but most have struggled to emulate the original Xbox OS and kernel. Microsoft developed the first Xbox with x86 hardware in mind, but the Xbox kernel was based on a custom and stripped down version of Windows 2000 with DirectX 8 support.

Unofficial emulators have tried to replicate this kernel for years, but so far only around 40 games have limited emulation support compared to the 900 games available for the original Xbox. Microsoft has its own proprietary emulation Xbox and Xbox 360 games, but it’s only currently available on Xbox One consoles and not on Windows PCs.

Alongside the Xbox leak, source code for a near-final version of Windows NT 3.5 has also appeared online. The source code includes all the necessary build tools, and should allow enthusiasts to dig into the old operating system. As Windows 3.5 support ended in December 2001, the operating system is only used in a small number of systems worldwide so a source code leak isn’t a significant security issue.

Microsoft has largely protected its proprietary Windows and Xbox source code over the years. Partial Windows 2000 and NT 4 source code leaked back in 2004, and even some Windows 10 source code was posted online in 2017. We asked Microsoft to comment on the Windows NT 3.5 source code leak, but the company says it has nothing to share about this particular incident.