A computer program that captures the keystrokes of a computer user and stores them. Modern keyloggers can store additional information, such as images of the user's screen. Most malicious keyloggers send this data to a third party remotely (such as via email).

    Keystroke logging 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.