Don't worry, you still have to give your permission for it to actually install.
Windows 10 is so revolutionary that it will soon download itself to your PC.
Microsoft early next year plans to make Windows 10 a "Recommended Update" for users of Windows 7 and Windows 8.1.
That means Microsoft will push the new operating system onto PCs that have kept the default Windows Update settings. (Windows Update is what Microsoft uses to distribute software updates like patches and new drivers.) PC owners will still have to approve the actual installation, of course—you're not going to go to bed with Windows 7 and wake up with Windows 10 without your knowledge—but the necessary files will be quietly downloaded in the background, ready to update your PC with the click of a mouse.
Microsoft says it wants as many users as possible on Windows 10 because it's "familiar, safer, faster, and full of innovations." Decoding that a bit, that means the Start menu is back after a brief hiatus in Windows 8; new safety features like Device Guard scan apps before they're run for the first time to ensure that they're not laced with malware; and features like Windows Hello let users log into their PC by having a webcam scan their face.
Having more and more PCs on Windows 10 also makes the platform more attractive to app developers, who can create apps that run on PCs and mobile devices with only a few tweaks to the underlying code.
It should be noted that although "mainstream support" of Windows 7 ended in January (meaning it won't receive any more shiny new features), Microsoft will still issue patches and other bug fixes for the operating system at least through January 2020; Windows 8 will be similarly patched through 2023.