A portion of Microsoft’s Windows 10 source code has leaked online this week. Files related to Microsoft’s USB, storage, and Wi-Fi drivers in Windows 10 were posted to Beta Archive this week. Beta Archive is an enthusiast site that tracks Windows releases, and asks members to donate money or contribute something Windows-related if they access a free private FTP full of archived Windows builds. The leaked code was published to Beta Archive’s FTP, and is part of Microsoft's Shared Source Kit.

“Our review confirms that these files are actually a portion of the source code from the Shared Source Initiative and is used by OEMs and partners,” reveals a Microsoft spokesperson in an email to The Verge. While The Register claims 32TB of data, including unreleased Windows builds, has been leaked, The Verge understands most of the collection has been available for months, or even years. The Register also claims the source code leak is bigger than the Windows 2000 leak from 2004, but The Verge understands this is inaccurate and that the Windows 10 source code leak is relatively minor.

An embarrassing leak for Microsoft

The leak will be embarrassing for Microsoft, but the source code itself is already shared with partners, enterprises, governments, and other customers who choose to license it through the Shared Source initiative. Microsoft’s Windows 10 Mobile Adaption Kit was also included in the leak, alongside some Windows 10 Creators Update builds, and some ARM-based versions of Windows 10.

Beta Archive owner Andrew Whyman has revealed the source code was just 1.2GB in size and has been removed. In an email to The Verge, Whyman says Microsoft has not forced the site to remove the code and that “we have removed the file under our own decision.”

The source code leak comes after two Microsoft-related arrests

The source code leak comes just a day after two men were arrested in the UK as part of an investigation into unauthorized access to Microsoft’s network. Detectives executed warrants to arrest a 22-year-old man from Lincolnshire, and a 25-year-old man from Bracknell. The Verge understands both men have been involved in collecting confidential Windows 10 builds, and that at least one is a donator to the Beta Archive site. A spokesperson for Thames Valley police refused to provide more information on the arrests to The Verge, and would not confirm the two identities of the individuals.

It’s not clear if the arrests are directly linked to the source code leak, but Microsoft is evidently concerned about some potential intrusions into its networks by Windows enthusiasts. The alleged offences took place between January and March, and a large dump of confidential Windows 10 builds was leaked to Beta Archive on March 24th. An administrator of Beta Archive, named only as "mrpijey," revealed "with the help of members (whose names shall never be mentioned) I've downloaded a whole lot of Windows Insider builds of Windows 10 directly from Microsoft" at the time of the leak. Ars Technica also reports that Microsoft’s build systems may have been hacked in March.

Microsoft has avoided, most of the time, lots of Windows 10 build leaks thanks to its Insider program that lets testers access early copies of the operating system. In the past, the software giant has aggressively pursued Windows leakers, and the company even scanned a bloggers Hotmail account to track down a Windows 8 leak once.

The Verge has reached out to Microsoft to comment further on the arrests, and we’ll update you accordingly.

Update, 6:25AM ET: Article updated to clarify Beta Archive description.