Keylogger

Keystroke logging (often called keylogging) is a diagnostic used in software development that captures the user's keystrokes. It can be useful to determine sources of error in computer systems. Such systems are also highly useful for law enforcement and espionage -- for instance, providing a means to obtain passwords or encryption keys and thus bypassing other security measures.

Keystroke logging can be achieved by both hardware and software means. Commercially available systems include devices which are attached to the keyboard cable (and thus are instantly installable, but visible if the user makes a thorough inspection) and also devices which can be installed in keyboards (and are thus invisible, but require some basic knowledge of soldering to install). Writing software applications for keylogging is trivial, and like any computer program can be distributed as a Trojan horse or as part of a virus or worm.

It is also said that using an onscreen keyboard is a way to combat these, as it only requires clicks of the mouse. That is, however, false information, because a keyboard event message must be sent to the external target program to type text. Every software keylogger can log the text typed with an onscreen keyboard.

This article is adapted from: wikiPedia.com.