When you upgraded to Windows 10, did you read the license agreement? Be honest! If you did, you may have noticed a clause that gives Microsoft permission to detect any illegally obtained software or hardware and disable it.
Technically, the license agreement isn't for Windows 10, but it applies to you if you have a Microsoft account or use Cortana, the new Windows 10 smart assistant (one of the operating system's most-hyped features). The license says Microsoft "may automatically check your version of the software and download software update or configuration changes, including those that prevent you from accessing the Services, playing counterfeit games, or using unauthorized hardware peripheral devices."
So if you're playing a copy of Halo that you downloaded via a torrent, Microsoft retains the right to disable your program. And it's not clear what they mean by "unauthorized hardware peripheral devices," though they could be referring to uncertified gaming controllers.
The technology site Alphr speculates that the license agreement language was intended for Xbox and Xbox Live, and transferred over for Windows 10 services. Alphr doesn't believe Microsoft will really be searching PCs running Windows 10 for pirated games. But still, better safe than sorry - and we never encourage anyone to pirate software of any kind.