Several users have reported an issue in which the cursor moves unexpectedly and without user input under Mac OS X 10.6.x (Snow Leopard). In these cases, the cursor may continue to move even when the mouse is physically disconnected. Users have also reported that the issue remains after switching mice (both wired and Bluetooth) and surfaces, making plausible that this is a software-related issue.
Apple Discussions poster musicwind95 writes: “My mouse cursor moves randomly around the screen, usually all the way across and almost always to one of the screen corners, in which I have hot corners enabled.”
Although this problem is generally innocuous, it can cause significant issues in some cases, including inadvertent scrolling of web pages or accidental file selection/deletion (if the cursor unexpectedly moves as a user is attempting to interact with a specific file).
Although anecdotal evidence suggests that, in most cases, this is not a mouse-surface issue, some users have reported success with placing a white sheet of paper underneath the mouse.
Some users have also reported that turning off secondary displays mysteriously resolves this issue, albeit not a viable permanent workaround.
A few users have reported at least temporary success with resetting PRAM/NVRAM.