Look out, Siri. Watch your back, Google Now. Here comes Cortana.

At its annual Build 2014 conference on Wednesday, Microsoft took the wraps off Windows Phone 8.1. The new features include a personal digital assistant called Cortana. 

Cortana is Microsoft's challenge to voice-activated services such as Google Now and Apple’s Siri. The new Cortana will be powered by Microsoft's Bing search engine.

Users will be able to use a feature called a "Notebook" which will let them decide exactly which things Cortana should keep track of. They can also select quiet hours during which Cortana won't bug them. Cortana can also be expanded to track services such as Yelp, Facebook, Hulu and Skype.

Windows Phone 8.1 also has new features for personalizing the home screen. 

According to the Next Web, Joe Belfiore, vice president of Microsoft's operating systems group, called Windows Phone "the most personal smartphone."  

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