Microsoft has been forced to apologise to early adopters in its Windows Insider program after it accidentally released problematic builds from internal development branches.
The Windows Mobile update is especially damaging to users as it bricks devices, causing them to constantly reboot, Microsoft software engineer Dona Sarkar said in a mea culpa.
The only way to recover from the reboot loop is to use the Windows Device Recovery Tool and re-flash the phone.
Desktop Windows Insider users weren't as negatively impacted, but Sarkar said the build - which "was never intended to go out" to the early adopters - "may include issues that impact the usability of your PC, more so than normal builds we give you".
Sarkar did not specify what the issues for desktop PCs were, but said there was no need for drastic recovery measures, and desktop users could just wait for the next Windows Insider build to roll out.
Users who want to roll back the installation of the unintentionally released build 16212 of Windows 10 have 10 days to do so, Sarkar said. If users have deleted the earlier installation with Disk Cleanup, they can't go back to an earlier build.
Windows Insider is an opt-in program for Windows 10 and Windows 10 Mobile that Microsoft initiated in 2014.
Microsoft operates three internal rings for build releases: Canary, which sees daily updates; the Windows and Devices Group ring; and the wider Microsoft ring.
Builds that have made it through the internal chain are cleared to reach users outside Microsoft in the external Fast ring; if no issues are found, the builds reach the Slow ring.
The safest and most stable ring is called Release Preview, which was introduced last year. It provides patches and bug fixes for existing versions of Windows 10, but delays delivery of new features until after they have been cleared by testers in the Slow ring.
Microsoft said it won't release any further Windows Insider builds this week.
