# What is a data breach?

A data breach is any security incident in which data is lost, stolen, destroyed, changed or seen by someone who should not see it. It does not need a hacker: an email with customer data sent to the wrong address is a breach too. Under GDPR, a breach involving personal data must be reported to the supervisory authority within 72 hours of becoming aware of it, unless it is unlikely to cause risk to people, and affected people must be told when the risk is high. IBM's Cost of a Data Breach 2025 report puts the average global cost at USD 4.44 million.

FAQ: [What is…? Network and security terms](https://netsenx.com/en/faq/glossary) · https://netsenx.com/en/faq/what-is-a-data-breach

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