A keylogger is a small software which you can install on any windows system. Once installed, it can record the keystrokes pressed on any pc. This means that anything the victim is going to write using his keyboard, it is going to get recorded. It includes email, passwords, phone number and other sensitive information. This inormation is then sent to the hackers email address and he can use the login information to hack into the facebook account of the victim. This methods is fairly easy provided you have access to the computer or device of the person you intend to hack. It requires no programming skills and is one of the most easy method to hack a facebook account.