Keyloggers take two primary forms, either as hardware adapters or software applications. This chapter will primarily focus on keyloggers as software applications. That said, it is important to be aware of the use of hardware keyloggers from a security perspective in the digital forensics and network security fields.
Hardware keyloggers can come in a variety of packages, using different methods to capture user data. One method is through interfacing with the keyboard or another IO (input/output) device before it connects to the computer. Sitting in the middle of the keyboard and computer, this device will capture the information as signals sent between the keyboard and computer. These "man-in-the-middle" keyloggers can be both wired and wireless. A fairly common application of hardware keyloggers might be seen with ATMs or other payment devices where a fake pin pad or intervening board is placed to intercept pin numbers entered into the machines...