Windows 10, by default, sends everything you search for in the Start Menu to their servers to give you results from Bing search—so you better make sure that you don’t type anything private into your own PC’s Start Menu. Or, you could just disable the Bing integration in the Start Menu.
Update: We now have a new solution that works in modern versions of Windows 10! We tested this method with Windows 10’s October 2018 Update.
It’s worth noting that Android’s default search and even iOS will also send your search results to their servers to try and get more relevant results—but somehow it seems different when you’re on your personal computer in your house trying to search through your personal files.
We’re definitely glad that they included a way to easily disable the web integration—it’s just worth noting that if you want to use Cortana, you don’t have any choice in whether the Start Menu uses Bing, so you’re going to have to disable Cortana to disable the web integration.
How to Disable Bing Integration in the Start Menu
You must edit the Windows registry to disable web searches in the Start menu.
Here’s our standard warning: The Registry Editor is a powerful tool and making the wrong change can make your system unstable or even inoperable. This is a straightforward change and, if you follow the instructions, you should be fine. But if you’ve never used it before, consider reading about how to use the Registry Editor. We always recommend backing up your Registry (and your computer) before making changes.
To start, open the Registry Editor by hitting Start and typing “regedit”. Double-click the “Registry Editor” shortcut that appears (or press Enter) and click Yes to the UAC prompt.
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Source: How-To Geek