Microsoft has mistakenly offered an interior Windows 10 build to users in the Windows Insider program ring.

Windows 10 build 18947, which hasn't passed internal validation to become pushed to insiders, was shipped via Windows Update to all rings in Microsoft's testing program.

While originally it looked like the release targeted 32-bit systems only, users on reddit claim they received the same surprising build on 64-bit machines too.

Build no more up for grabs

Microsoft explains inside a statement the blunder was caused by a so-called "configuration change" that allowed the build to be sold to external rings. Quite simply, it had been only said to be pushed to internal rings where Microsoft engineers could test this build, however it eventually made it to public testers too.

"We actively test and validate all of our preview builds internally before sharing them externally, however a configuration change allowed this build to release to multiple rings simultaneously, including external rings," the organization notes in a Microsoft Community post where additionally, it shared instructions regarding how to roll back for users who installed this build.

"We have made the required remediation within our Flighting service and have implemented additional changes to assist prevent out of this happening in the future. We apologize for just about any troubles this might have caused for affected Insiders and thank you for assistance in bringing this to our attention therefore we might make the required changes as soon as possible."

The build is not readily available for download from Windows Update, and Microsoft tells insiders to avoid setting it up, particularly if the update happens to be pending.

There's no ETA at this time regarding when a new build should ship, however i expect someone to go live next week considering that in the next couple of days Microsoft engineers could be busy fixing this blunder.