The Register is reporting that a massive trove of Microsoft’s internal Windows operating system builds and chunks of its core source code have leaked online.

It is believed the data has been exfiltrated from Microsoft’s in-house systems since around March.

The leaked code is Microsoft’s Shared Source Kit: according to people who have seen its contents, it includes the source to the base Windows 10 hardware drivers plus Redmond’s PnP code, its USB and Wi-Fi stacks, its storage drivers, and ARM-specific OneCore kernel code.

Obviously, this will make it easy for people to find weaknesses in Windows 10 that they can exploit to create viruses, malware, ransomware, and worse.