I was in the middle of doing some housekeeping when Finder logged out on its own and prompted me to log in again. When I did, my wallpaper had been reset to the Sierra default. More curiously, three instances of the Flash installer package had been mounted to the desktop, and Chrome had launched (it is not my default browser). Very odd. Any idea what may have happened? I was not connected to WiFi, and was cleaning up old archived iMessage conversations when it happened.