Q My mouse pointer, whether using my normal Magic Mouse or other models, keeps jumping to the top left corner of my screen, making work almost impossible. What is causing this?
A You are most probably using your mouse on an unsuitable surface, it being light or reflective, which tends to confuse optical mice. The best surface for mousing is dark, matte and of even colour, such as a brown plastic office desk overlay.
If that does not help, restart with the Shift key held down, as this is then most probably a rogue third-party extension, which will be disabled in Safe mode. You will next need to work out which product is responsible, and either uninstall or update it.
Updated from the original, which was first published in MacUser volume 28 issue 03, 2012.