Microsoft has confirmed in an email to The Verge that indeed a portion of confidential Windows 10 source code was leaked online. Around 32TB of leaked data files (compressed to 8TB) pertaining to Microsoft's Shared Source Kit were posted to Beta Archive earlier this week and this was first reported by The Register.
It is reported that the files related to Microsoft's USB, storage, and Wi-Fi drivers as well as Windows 10 Mobile Adaptation Kit and Creators Update builds were posted on the Beta Archive's FTP server.
Contrary to the claims made by The Register, The Verge reports that most of the unreleased Windows builds were available for months, if not years, and the source code leak is just minor.
Furthermore, Beta Archive owner Andrew Whyman has added more credence to The Verge's theory by confirming that the source code was just 1.2GB in size and not an 8GB compressed file as claimed earlier. Whyman also clarified that the file has now been removed from the site without any intervention from Microsoft.
It seems the source code leak is linked to the arrest of two men in UK, who have been accused of collecting confidential Windows 10 builds by hacking through the Microsoft network. Detectives involved in the case have identified the culprits wherein a 22-year-old man from Lincolnshire and a 25-year-old man from Bracknell have been arrested.
The spokesperson for the Thames Valley Police after the arrests has refused to divulge any further identity information on the accused in the case. However, it is confirmed that at least one is a donator to the Beta Archive site.
"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 report added.
