Microsoft just announced their virtual assistant software for Windows Phones, and the connection to Halo isn’t just her name:
Cortana is named after a virtual character in Halo, Microsoft’s science-fiction video game series, that uses her encyclopedic knowledge about the universe to help the game’s protagonist, Master Chief. The actress, Jen Taylor, who does the voice for the character, also provided recordings for the phone assistant’s voice.
http://bits.blogs.nytimes.com/2014/04/02/meet-microsofts-cortana-a-more-personal-siri/