I would much appreciate any help or comments regarding the following issue: I use MacBook Pro i7, 8 GB, ML 10.8.4., MB < 1 year old. When I move three fingers up and down the trackpad twice and tap once immediately after this, the OS brings up a login screen. (I obviously don't want this...). I am not quite sure whether it started after upgrade to 10.8.4., but it seems like a new problem. Is it a flaw, a mechanical problem with the trackpad, or a feature? Thanks!