Flip the mouse upside down. If it continues to move (do not wave your hand over it!) then it's defective.

If it stops then it doesn't like the surface it's on. Try a sheet of paper or some other mouse pad.

That's the troubleshooting for it creeping when you feel it shouldn't.

Lastly for wild movements, unplug it and uninstall ALL logitech software. Uninstall all MOUSE DRIVERS and use the windows stock driver it finds on its own.

Bob