Proof of damage is the evidence that shows harm really occurred and explains how it happened. In cyber security, that can include system logs, timestamps, altered files, exfiltration records, screenshots, outage reports, and financial records. It is not enough to say an attack happened; investigators often need to show the impact, the timeline, and the link between the intrusion and the loss.
This matters because liability, insurance claims, incident response, and regulatory reporting often depend on demonstrating real damage. In a ransomware case, proof may show encrypted systems, interrupted operations, and data theft. In a data breach, it may show which records were accessed and whether they were exposed. Defenders strengthen proof by preserving logs, keeping backups, documenting actions taken, and maintaining chain of custody so the evidence remains reliable in court or internal review.