A second important weakness in using passwords is that they must be "uttered" to be used, and there is always a chance of eavesdropping when they are uttered. The lowest-tech form of eavesdropping is to watch as someone types a password. There is an etiquette around the operation of ATMs. Even when there is a substantial line, the second person stands a discreet distance behind the person operating the machine and looks away. The etiquette is not so highly evolved in an office environment, and it often isn't difficult to pick up passwords this way. The only prevention beyond training people to be more paranoid is to pick passwords involving shift and control characters so more fingers are involved.