A Keylogger is a program that is designed to intercept and log keystrokes. Attackers use keylogging functionality in their malicious programs to steal confidential information (such as usernames, passwords, credit card information, and so on) entered via the keyboard. In this section, we will mainly focus on the user-mode software keyloggers. An attacker can log keystrokes using various techniques. The most common methods of logging keystrokes are using the documented Windows API functions: (a) Checking the key state (using the GetAsyncKeyState() API) and (b) Installing Hooks (using the SetWindowHookEX() API).