A coworker had just bought a refurbished computer with Windows 7 OS and was dutifully applying updates. He noticed a new icon in the taskbar tray and clicked it. The program presented him with the opportunity to upgrade to Windows 10. It implicitly asked when would you like to download Windows 10? The dialog box offered two buttons labeled "Upgrade now" and "Upgrade tonight."
How about Never? That was not an option.
The Gwx.exe and GwxUX.exe programs make it easy for users to reserve their free copy of Windows 10. They appear after the user applies the update associated with KB3035583. And they disappear after the user uninstalls that update.
This "How To Geek" article describes it all in detail.
My previous post discusses why you might want to avoid upgrading.