A new Windows Phone 8.1 Update 1 aka GDR1 build is rolling out to devices with Windows Phone Preview for Developers. The update bumps the build version of the device to 8.10.14192.280.

Microsoft has called this a "critical update". The Windows Phone device will automatically be updated within 72 hours of downloading the update, if you do not do it. It seems to be some preparatory update to something critical, reports NPU.

Greg Sullivan, Microsoft's senior product manager, has announced via Twitter that the developer preview update is testing critical update capability.

To check the update manually, navigate to Settings>> Phone Update. The update will take 5 to 10 minutes to install and you will not be able to use the phone while it is installing.

Meanwhile, Microsoft has explained on its Community page what the critical update is and why users need to install the latest 8.10.14192.280 build.

"This update contains our usual scope of fixes and improvements. We're requiring this update so we can continue to test our update systems. The update will show as a "critical update" on your phone.

"Taking this update will get you to the latest build that we offer for the Windows Phone Preview for Developers program. This update will automatically install 72 hours after it's been downloaded—or you can install it sooner. If you want to opt out of the program or do not wish to take this update, open the Preview for Developers app on your phone and clear the Enable Preview for Developers check box."