The primary purpose of an intrusion prevention system (IPS) is to detect and prevent malicious activities or policy violations in network traffic in real-time. An IPS monitors network and system activities for signs of known threats, such as exploits or malware. When potential threats are detected, the IPS takes action by blocking or rejecting the suspicious traffic. This proactive defense mechanism is essential for protecting sensitive data and maintaining the integrity of networks, thus providing a critical layer of network security.