"Builds from some of our internal branches were accidentally released for PC and Mobile", reveals Dona Sarkar, Microsoft's head of its Windows Insiders program. These weren't just builds launching earlier than expected, they were builds never meant to reach the public. However, within 30 minutes another tweet from Sarkar advised Windows Insiders to not install any updates that were now being offered unless Microsoft told us about them along with a blog post describing the build. The company said the builds were pushed out to Windows Insiders because of an inadvertent deployment to the engineering system that controls which builds and which rings get doled out.
And now it seems that many users of Windows XP got the message, as new statistics show that XP's market share collapsed last month, dropping from 7.04 percent to 5.66 percent. However, that could take several days and definitely won't happen this week. Anyone who installed the build can either roll back to the previous release or wait until Microsoft publishes a new fast ring build. If Windows 10 testers installed the mobile build it forced phones into a reboot loop and bricked the device. Once that's done you have to re-join the Windows Insider Program and download a new build.
The said internal update, released for Windows Insiders, is known to contain bugs and broken things that might cause people's computer to experience crashes and run into a boot loop. Anyone on the Creators Update or newer will find these builds waiting for them - including those in the Slow and Release Preview rings - and your phone might even try to install them automatically if you're not paying attention.
If all else fails you could attempt a hard reset of the device by following these steps which are detailed over in this Microsoft Answer community forum post but your mileage may vary as this article is over three years old. 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.
"This build will *not* install on your device", Sakar says. Still, none of these rings are supposed to receive the internal builds released yesterday.