A software program that is designed to record and store every keystroke made on the computer. A key logger is often used as a sneaky way to steal passwords without the person knowing it's happening. Or it can be used to steal confidential information. A key logger can be combined with a communication program so that each key press is sent to a remote computer over the internet if that computer is online. Most security / anti-virus packages will try and detect if a keylogger is active on your computer.