Microsoft was forced to apologize late last night after a mistake led to some confidential and internal Windows 10 builds being released to the public. “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. “This happened because an inadvertent deployment to the engineering system that controls which builds / which rings to push out to insiders.”

Microsoft says it quickly reverted the issue and put blocks in place to ensure these development builds didn’t reach more people, but a “small portion” of Windows 10 users still received them. Worryingly, the accidental mobile build even reached retail devices outside of Microsoft’s Windows Insiders testing. If Windows 10 testers installed the mobile build it forced phones into a reboot loop and bricked the device. Testers will have to recover and wipe the device using the Windows Device Recovery Tool.

Windows 10 testers that installed the PC build, an internal Edge branch, will have to wait for Microsoft to publish a newer build or roll back using the recovery option in Windows 10 settings. “We apologize for this inconvenience and thank you for being a Windows Insider,” says Sarkar. Microsoft says it won’t be releasing any new builds this week, presumably as it’s working to ensure this surprising mistake doesn’t occur again.