Key loggers are available in a few different forms, ranging from software through to plug in hardware devices.

Basic keylogging software will record all visible characters, such as those you see on a document. Advanced keyloggers are able to record all hidden, or invisible, keys such as the "Shift" and "Ctrl" keys. Some will also provide a time/date stamp, and record what document or window the keystrokes were typed in.

Keylogger software is useful in a variety of applications, ranging from keeping the kids honest, to preserving documents as they are typed, and diagnostic testing of software. It is available as standalone software in a discrete form used for computer surveillance, and also as a standard application. Keylogging utilities are commonly bundled with advanced monitoring software as part of a complete computer surveillance package.

Unfortunately key loggers are commonly integrated into spyware applications, trojan horses, viruses, and worms, with the design of stealing information such as passwords and online banking details.

It is also documented that police departments and intelligence agencies make use of key logging applications embedded within trojan horses to obtain information from suspects.