A Man-in-the-Middle Attack (MitM) occurs when an attacker secretly intercepts and relays communication between two parties. This can happen over unsecured networks, allowing the attacker to eavesdrop, alter messages, or steal sensitive information like passwords and credit card numbers. To prevent MitM attacks, users should employ secure connections, such as HTTPS, and use VPNs for added protection. Regularly updating software and being cautious with public Wi-Fi can also help reduce the risk of falling victim to these types of attacks.