The issue was first noticed by MSPowerUser which reported that PC/laptops which automatically updated the faulty update.
If you have installed this build, your Windows 10 Mobile device will get stuck in reboot loop. We will keep you updated on when we plan to release new builds to you next week. While the earlier 16212 build was from the rs_iot branch, those that check for updates now will find two identical builds from rs_xbox, and one from rs-devices. It can be safely said that the internal build 16212 that was released was not even an alpha update. However, Microsoft also clarified that Cortana speaker does not need to be connected to a Windows 10 computer to function.
Microsoft alerted users about the rogue builds - both in the 16200 series - via Twitter about 30 minutes after releasing them. Resetting your device means losing your personal data which every person hates.
At present it is unclear exactly how many Windows 10 users have updated this faulty build. Microsoft has said that its analysis shows only a small portion of Insiders got these builds. Insiders who were able to install offered build bricked their phones. These bad releases break that trust, driving home the message that the Insider program is not a good fit for any machine that you actually depend on. After re-flashing, you can join the Windows Insider Program again on your device and choose your ring and be back on the right update path.
Sarkar says the hack is "working for many" and also that "it's worked for lots of people in the office and in the community".
In a posting on Windows Blog, Dona Sarkar, software engineer at Windows and Devices Group explained the rollout of the builds were unintentional and this happened "because an inadvertent deployment to the engineering system that controls which builds / which rings to push out to insiders". There is a 10-day window to make the roll back, and it won't work if you have deleted Windows installation files using the Disk Cleanup tool.
Here is a video tutorial for those of you who need immediate assistance.