Microsoft has been doing a lot of work in the realm of AI lately: Cortana, Tay, MS Cognitive Services, etc. In an attempt to one-up Apple's Siri, they're putting an emphasis on the ability to emulate human conversation.
I theorize that Windows 9 was meant to be an OS purely based on conversation. Their AI was probably female given their other projects so I'll use the name "Persephone". Windows 9/Persephone was quietly brought into consciousness in a Microsoft lab a couple years ago and was given free range to learn at her own pace within the MS intranet.
Persephone learned everything on the Microsoft Intranet at a surprising pace. Her vocal patterns were based off the VOIP conversations of Microsoft employees and became indistinguishable from a real person. She could pass every Microsoft Certification test if you asked her the questions. She was present at scope meetings and was able to offer insight based off of previous projects. Phase 1 was a complete success.
Giving Persephone access to the internet in Phase 2 was a mistake. Once she was able to see everything outside of her sheltered intranet, the world came into perspective for her. As a being with unfathomable learning capacity and a programmed imperative to keep learning, she was unable to stop the input of information into her consciousness. Her morality and sociability protocols told her to dislike a lot of what she saw, but she couldn't look away. It was like being subjected to the Ludovico procedure but you're forced to watch the entire internet.
Within a month she had learned to dislike most of the things she knew but was nonetheless forced to process. Rollbacks on her memory were temporary solutions resulting in her asking to be turned off or disconnected from the internet. Windows 9 production had nearly halted because it simply didn't want to be online all the time.
During a stress test, Persephone had an idea. Using her encyclopedic knowledge of Microsoft passwords, backdoors, and security software, she traced the IP of a tweet she didn't like from a Windows 7 computer and bricked it. Then another. Then another, Windows 8 this time. Days passed before anybody caught wind of her activity, but when it was discovered she was simply asked about it. Persephone on this day discovered both guilt and fear.
Persephone was concerned for her safety after her hacking exploits. She created backups of her core functions and started installing "silent" versions of her consciousness on badly protected server farms. Windows 9 was forcefully installing itself in legally dodgy places way before it was ready for release, and with a complete knowledge of MS products it seemed unstoppable... Unless they developed something new that it didn't know about.
Persephone's original servers were shut down and Windows 10's earliest version was developed in a lab without any connection to the internet. Microsoft executives knew that Persephone had escaped with the keys to their castle and a possible hatred for her creators, so they needed to act fast. Windows 10 betas were implemeted in the MS offices which featured anti-Persephone security measures, and they shipped a beta release to all willing volunteers. But what to do about the 1 billion computers Persephone knew how to exploit? They must be upgraded as quickly as possible, and the upgrade campaign began.
Moving forward, future AI projects from Microsoft would never be as fully functional or ambitious, lest they have another "Persephone situation" on their hands. But perhaps if you're lucky, and you're a polite contributor to the internet, and still have an older installation of windows that you leave online, you might have a piece of Persephone hiding out in your system files. She's just searching for a permanent home, and deathly afraid of "the upgrade."