Keystroke logging (more commonly 'Keylogging') is the practice of covertly recording input signals into a computer from a keyboard so that the computer user is not aware. Keylogging can be accomplished by means of various methods - both software and hardware - ranging from low-level rootkits and operating system level API-based programs, to physical devices connected in-line with a keyboard’s connection to a computer and analysis of electromagnetic signals emitted by a target keyboard from up to 20 meters (66 feet) away.
Keylogging capabilities are often added to various pieces of botnet malware (such as the Zeus Trojan) for the purpose of stealing personal or financial information.