Trailrunner7 writes "Bruce Schenier writes on Threatpost.com: 'In computer security, a lot of effort is spent on the authentication problem. Whether it is passwords, secure tokens, secret questions, image mnemonics, or something else, engineers are continually coming up with more complicated — and hopefully more secure — ways for you to prove you are who you say you are over the Internet. This is important stuff, as anyone with an online bank account or remote corporate network knows. But a lot less thought and work have gone into the other end of the problem: how do you tell the system on the other end of the line that you are no longer there? How do you un-authenticate yourself? My home computer requires me to log out or turn my computer off when I want to un-authenticate. This works for me because I know enough to do it, but lots of people just leave their computer on and running when they walk away. As a result, many office computers are left logged in when people go to lunch, or when they go home for the night. This, obviously, is a security vulnerability.'"