Windows 10 will send Microsoft data even when you tell it not to.

Several key Windows 10 features, including Cortana, could be sending identifiable information to Microsoft, according to tests by Ars Technica.

Windows 10 uses the web for many of its flagship features. You can search Bing, Microsoft's search engine, right next to the Start menu, or you can use Cortana, Microsoft's digital voice assistant to perform actions across the system.

But every time your machine interacts with these features, it sends out an identifier unique to your system that can be linked back to you. The link is made, and user information shared with Microsoft, even when the user turns privacy settings on, according to the report.

Microsoft says it collects data to improve services, but no specific data like search terms is sent to the company.

"As part of delivering Windows 10 as a service, updates may be delivered to provide ongoing new features to Bing search, such as new visual layouts, styles and search code. No query or search usage data is sent to Microsoft, in accordance with the customer's chosen privacy settings. This also applies to searching offline for items such as apps, files and settings on the device," they said in the emailed statement.

Collecting usage data is something virtually every tech company does. But if you want to stay 100% percent offline using Windows 10, you might have some trouble doing so.