A keylogger, sometimes called a keystroke logger, key logger, or system monitor, is a hardware device or small program that monitors each keystroke a user types on a specific computer's keyboard.
A keylogger program does not require physical access to the user's computer. It can be downloaded on purpose by someone who wants to monitor activity on a particular computer or it can be downloaded unwittingly as spyware and executed as part of a rootkit or remote administration (RAT) Trojan horse. A keylogger program typically consists of two files that get installed in the same directory: a dynamic link library (DLL) file (which does all the recording) and an executable file (.EXE) that installs the DLL file and triggers it to work. The keylogger program records each keystroke the user types and uploads the information over the Internet periodically to whoever installed the program.
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