Microsoft's Windows Phone assistant is actually called Cortana

Microsoft has officially unveiled its own answer Siri and Google Now for Windows Phone 8.1, and the rumours were true: it is genuinely called Cortana.

Cortana was introduced today by Microsoft's Joe Belfiore onstage at the company's annual Build conference in San Francisco, with the character named--just in case you don't already know--after Master Chief's AI partner from the Halo series.

The voice of Cortana sounded like it was being provided by voice actress Jen Taylor, who also lends her vocal chords to the character in the games. If it wasn't Taylor, it sounded like a particularly uncanny impression.

"Cortana is powered by [Microsoft search engine] Bing," added Belfiore. I'm not sure how 343 Industries is going to write that into Halo 5, mind.

Cortana on Windows Phone can perform many of the features that we've come to expect from these types of services, such as setting appointments and searching the web. One of Cortana's unique points, however, is that it can understand and answer follow-up questions: the app answered "How about in celsius?" after responding to the initial question of what the weather was like in Las Vegas.

In a bit of typical on-stage banter, Belfiore also asked Cortana "what's the story for the next Halo game?"

The answer? "I'm quite certain you don't have proper security clearance for that information." Drat.

Cortana will be released first as a beta in the US, and the service will reach the UK and China shortly after the full launch.