An early build of Microsoft's Windows 8.1 Update 1, a tweaked refresh of last fall's revamp to 2012's original Windows 8, has leaked to pirate websites, according to Web searches.

Windows 8.1 Update 1 is the name given by others to what Microsoft is expected to ship this spring -- perhaps around the time of its Build developers conference, which runs April 2-4 -- as a first-round refresh of 2013's free update to Windows 8.

Update 1 appears to be another set of user interface (UI) and user experience (UX) changes designed to make the two-headed operating system easier to navigate and operate for customers with traditional non-touch personal computers, those who rely on a mouse and keyboard rather than their fingers.

Among the most notable changes are ones that let users "pin" touch-first apps -- dubbed "Metro" by most even though Microsoft abandoned the term 18 months ago -- to the classic desktop's taskbar; display search and power buttons on the tile-style Start screen; and add a sort-of-standard Windows title bar to Metro apps that include targets for closing, minimizing and snapping the app.

According to several file-sharing websites, the leaked build -- identified as version 6.3.9600.16596 -- weighs in at about 3.8GB and was compiled in mid-January.

On Sunday, Wzor expanded on what it found within a more recent build, 6.3.9600.16606, that was compiled on Jan. 26, or eight days ago. The site had first spilled some secrets of that third-round test build last Thursday.

The preliminary versions that Wzor obtained, and that file-sharing services have posted for download, were meant for Microsoft's OEM (original equipment manufacturers) partners, the computer vendors that design, assemble and sell new PCs, tablets and crossover devices that combine traits of both.

In its initial report last week, Wzor claimed that Microsoft had enabled the "boot to desktop" setting, currently an option, as the default, so that users would bypass the Start screen and the flat UI that relies on colorful tiles and runs mobile-style apps rather than traditional Windows applications. One analyst called that reversal a "a milestone in the proof that the strategy didn't work," referring to Microsoft's plan to force Windows 8 users to at least transit the Start screen on their way to the desktop.