Maybe I developed this habit because I'm a systems administrator, sometimes have sensitive information on my screen, and have colleagues around me who will send email from my mail program to the team if I walk away from my computer and leave my screen unlocked, but I ALWAYS lock my screen even if I'm walking away for 15 seconds. Do you lock your monitor when you get up from your computer? Even when it is just to get a cup of coffee? How many minutes until your screen saver turns on? Is your screen saver password protected?