A denial of service (DoS) attack is an attempt to prevent legitimate users from accessing a service or a resource by overwhelming it with malicious traffic or requests. A hacker can use a lockout capability to start a DoS attack by repeatedly sending invalid authentication attempts to a system or an application that has a policy of locking out accounts after a certain number of failed attempts. This can result in locking out legitimate users from accessing the system or the application, or consuming the system's resources and slowing down its performance. A dictionary attack is a type of brute force attack that tries to guess passwords or encryption keys by using a list of common or likely words. A ping flood attack is a type of DoS attack that sends a large number of ping packets to a target system, hoping to consume its bandwidth or processing power. A man-in-the-middle (MITM) attack is a type of attack that intercepts and alters the communication between two parties, without their knowledge or consent. References: CISSP CBK Reference, 5th Edition, Chapter 6, page 323; CISSP All-in-One Exam Guide, 8th Edition, Chapter 6, page 293