The confidential builds include test versions of the operating system including unreleased 64-bit ARM versions of Windows, bug-hunting builds with private debugging symbols, and multiple versions of the Windows 10 Mobile Adaptation Kit, which Microsoft uses to get Windows 10 running on various mobile devices.
The leak also contains Microsoft's Shared Source Kit, which is only meant for use by hardware makers, OEMs and trusted enterprise and government partners. This kit provides the source code to the base Windows 10 hardware drivers, PnP code, the WiFi and USB stacks, storage drivers, and ARM-specific OneCore kernel code. The Beta Archive data dump included 1.2GB of Shared Source Kit files. Hackers are most likely already scanning the confidential code to discover potential security vulnerabilities.
The Register reports Beta Archive has deleted the data dump and is going to do a full review of its content:
The source kit is supposed to be available to only "qualified customers, enterprises, governments, and partners for debugging and reference purposes."A Microsoft spokesperson confirmed the files include a portion of the source code from the Shared Source Initiative.
In a statement, Beta Archive said: "The 'Shared Source Kit' folder did exist on the FTP until [The Register's] article came to light. We have removed it from our FTP and listings pending further review just in case we missed something in our initial release. We currently have no plans to restore it until a full review of its contents is carried out and it is deemed acceptable under our rules."