Speaking of Cyanogen OS:
Following the Cyanogen OS 12.11 update for the OnePlus One, you may have noticed something worse than the automatic inclusion of Cortana. Now upon selecting a file without a set default application, you will see adverts for Microsoft apps and services on the "open with" menu.
I feel like a broken record player at this point, but don't trust these guys. Selling out to Microsoft has never done anyone any good.