Cortana, basically the definition of a virus from microsoft, the most useless terminate and stay resident software you can find in the universe.  you can close it, kill it, try to delete it only to have it re install and enable and activate itself once again.   I hate it, never used it once, have alt+f4 killed it dozens of times just because I enjoy killing the app over and over again hoping its developers are monitoring how many times their shitty app was terminated.