I installed Norton 360 security yesterday and since then a message has been regularly appearing at the bottom right of my screen.
It reads 'Norton is currently performing background tasks'. When I move the mouse this message disappears only to appear later.
More than likely it's performing a scan if the computer is left idle for a certain amount of time, it's actually not a bad thing to have enabled, but if you really want to switch it off then open norton, goto settings and under Computer Scans, select Off from the drop-down menu next to Idle Time Scan and click ok.