A zero-day attack occurs when cybercriminals exploit unknown software vulnerabilities before developers can issue patches. These attacks target large organizations, government agencies, IoT devices, and high-value individuals. Famous incidents include attacks on Microsoft Windows, Google’s Android services, and the 2019 DNC breach. Preventative measures include multi-layered security controls, regular vulnerability scanning, intrusion detection systems, and timely patching. Developers watch for abnormal software behavior, exploit patterns, and vulnerability signatures. Recovery strategies inv