An Indicator of Compromise (IOC) is any piece of evidence that suggests a computer system or network may have been breached by cyber attackers. IOCs include suspicious files, unusual network traffic, unfamiliar IP addresses, or unexpected changes to system settings. Security professionals use IOCs to detect, investigate, and respond to potential security incidents, helping organizations identify and limit the damage from cyber threats. Recognizing IOCs is essential for maintaining strong cybersecurity defenses and preventing further attacks.