- Keylogging covers any act that results in the keystrokes of a user getting recorded, typically without his knowledge, for the purposes of obtaining vital and private information, such as their passwords, or bank or credit card information. The use of a keylogger is usually considered illegal under surveillance and wiretapping laws, even if the computer is yours.
- The most common keylogger that people find themselves infected with is a software-based one. They can hide within other computer viruses and Trojan horses, and begin collecting data as soon as the base software is run or installed. A software keylogger hides within the system memory and creates a log of the keystrokes made; and when it is less likely to get caught, it will send the file out. Other software loggers will only store the data on the computer, and require the computer be manually accessed to get the files.
- Hardware keystroke monitors are attached to the computer keyboard either between the PC and keyboard cable, attached to other parts of the hardware, or even inside the keyboard, to interface with electronics directly and covertly. These keystroke loggers will record the key presses and either transmit them or store them for later retrieval. This is the main downside to hardware methods; any retrieval of the stored data will cause the risk of detection.
- Software and hardware methods are not the only ways to log keystrokes on a machine; there are much harder-to-detect methods which make use of physics to figure out the keys pressed. One such method employs the use of a sensor on the ground line to the computer. Every keystroke generates a signal, which experiences a tiny amount of "leaking" to the ground terminal. Someone who is experienced in reading and measuring the signals could then reconstruct keystrokes. Another method requiring computation is an acoustic analysis of typing sounds, where frequency analysis is utilized to determine which sounds correspond to which keys. The easiest method of keystroke logging is a secret camera with full view of the keyboard.
- There are a number of things that can be done to counter keyloggers. Software keystroke loggers that hide on systems can be located with anti-spyware and anti-viral softwares, if such software is kept up-to-date. Many hardware loggers that attach to a keyboard are easy to spot as a extra element behind the computer. On-screen keyboards and web keyboards also provide protection, as the base for keystrokes is not the keyboard but the mouse and program elements.
