Cortana hasn't been resting on its laurels. It leapt out of Halo to become a virtual assistant on Windows 10, expanded further still to Android and iOS, and now has the ability to appear over the Android lockscreen with information about the weather, upcoming appointments, and other goings-on. Updates to Windows 10 have also given Cortana the ability to find tasks in your email, for example, or proactively display apps in Microsoft Edge.
All those updates came after Microsoft removed the ability to easily disable Cortana with the Windows 10 Anniversary Update in August 2016. You still have some control over the information available to Cortana--you can opt not to let it access your email, calendar, and messages, for example--but now you have to fiddle with your registry (if you use Windows 10 Home) or group policy settings (if you use Windows 10 Pro) to make Cortana disappear.
Combine that with Microsoft's decision not to update Windows 7 or Windows 8.1 to support Intel's Kaby Lake or AMD's Ryzen processors, thus ensuring all but the most resilient of Windows users will make the jump to Windows 10 in the near future, and Cortana's expansion feels as inevitable as the parasitic Flood it helped combat in the Halo series. Whether that's a good or bad thing depends on how Microsoft decides to use Cortana's nigh ubiquity.
The Electronic Frontier Foundation criticized Microsoft for Windows 10's data collection, especially with Cortana, in August 2016:
The trouble with Windows 10 doesn’t end with forcing users to download the operating system. Windows 10 sends an unprecedented amount of usage data back to Microsoft, particularly if users opt in to “personalize” the software using the OS assistant called Cortana. Here’s a non-exhaustive list of data sent back: location data, text input, voice input, touch input, webpages you visit, and telemetry data regarding your general usage of your computer, including which programs you run and for how long.
While we understand that many users find features like Cortana useful, and that such features would be difficult (though not necessarily impossible) to implement in a way that doesn’t send data back to the cloud, the fact remains that many users would much prefer not to use these features in exchange for maintaining their privacy.
It's important to note that sharing information with Cortana is opt-in; you have to give the assistant permission to access your data. That isn't true of everything on Windows 10, which by default collects plenty of information about you, but at least the virtual assistant won't just read your email without permission. The question is whether or not Microsoft will change this in the future, just like it nixed the ability to easily disable Cortana back in August.
Cortana's increasing availability could raise fears about the virtual assistant's privacy settings. Microsoft continually demonstrates its commitment to Cortana with announcements like the one today, which made it even easier to use Cortana on a software platform Microsoft doesn't even control. The assistant often gets more features with greater control over the system, such as the ability to shut down, restart, or sign-out of a Windows 10 device.
Cortana is expanding. It's available on more platforms, it's regularly updated with new capabilities, and soon it will be core to your Windows experience, even if you held off updating to Windows 10, simply because new hardware won't be compatible with older versions of the operating system. If you're skeptical about the virtual assistant's respect for your privacy, that might not be the good news Microsoft likes to present it as.